Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/acd617

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP publishing  

DOI： 10.1088/1402-4896/acc4f2

Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：電気学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optica Publishing Group  

We propose a magneto-optical diffractive deep neural network (MO-D²NN). We simulated several MO-D²NNs, each of which consists of five hidden layers made of a magnetic material that contains 100 × 100 magnetic domains with a domain width of 1 µm and an interlayer distance of 0.7 mm. The networks demonstrate a classification accuracy of > 90% for the MNIST dataset when light intensity is used as the classification measure. Moreover, an accuracy of > 80% is obtained even for a small Faraday rotation angle of π/100 rad when the angle of polarization is used as the classification measure. The MO-D²NN allows the hidden layers to be rewritten, which is not possible with previous implementations of D²NNs.

DOI： 10.1364/oe.470513

Publishing type：Research paper (scientific journal)   Publisher：Optica  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Architectures based on multi-bit magnetic domain walls (DWs) take advantage of the fast speed, high density, nonvolatility, and flexible design of DWs to process and store data bits. However, controlling multi-bit DWs driven by electric current at an ideal position remains a significant challenge for developing integrated spintronic applications with high reliability and low power consumption. We exhibit the possibility of driving fast and stable multi-bit DWs at low current density without an in-plane external magnetic field in Fe-rich GdFeCo magnetic wires. When an in-plane magnetic field is applied in the wire direction, the front edge accelerates, although the rear edge decelerates, and the recorded data are destroyed. Hence, this method is not practical. Here, the DW speed of the multi-bit DWs is 1500 m/s under a low current density of 29 × 10¹⁰ (A/m²). A straight DW shape is required to accurately read the bits of information by the tunneling magnetoresistance head in real DW memory devices. Moreover, we demonstrate that the DW position is related to the DW shape after injecting a pulse current into the magnetic wire. A straight DW shape is exhibited for 3 ns pulse duration width, while the DW shape became rounded for 30 and 50 ns pulse duration widths. Our finding provides a practical concept for multiple-bit-per-cell memory and presents a viable platform for DW memory applications.

DOI： 10.1063/5.0086380

Publishing type：Research paper (scientific journal)   Publisher：Frontiears  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

The spin Hall effect, Dzyaloshinskii-Moriya interaction, Rashba effect, etc. are extremely important effects for the development of the conduction phenomenon of spin electronics due to the breaking of the spatial inversion symmetry of the hetero interface made of heavy metals such as Pt and W. These are due to SOI (spin-orbit interaction). Most of these studies have been conducted in the frequency domain below GHz, and there are few studies in the energy domain of light. Therefore, in the region of light energy, the magnetic optical Kerr effect spectra of the TbCo/Pt hetero-structured film with large SOI from the Pt interface and the TbCo/Cu hetero-structured film with small SOI from the Cu interface were measured, and the permittivity tensors were investigated respectively. As a result, in the TbCo/Pt hetero-structured film, the dielectric constant off-diagonal component real part of the thin TbCo layer increased about twice as much as that of bulk TbCo in the energy region smaller than 2.5 eV. However, this increase was not observed in the TbCo/Cu hetero-structured film. This result suggests that the influence of the Pt hetero interface where the spatial inversion symmetry is broken may appear even in the energy region of light. Furthermore, it has been confirmed that TbCo/W hetero-structured film using W with a large SOI has the same increasing effect as that of the TbCo/Pt.

DOI： 10.3389/fphy.2022.949571

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

To achieve a 20 Gbps data rate using the upcoming 5G communication standard, it is crucial to recognize a domain wall (DW) velocity (v_DW) of 1200 m s⁻¹.

DOI： 10.1039/d2ma00273f

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Publishing type：Research paper (scientific journal)   Publisher：AIP  

Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0064346

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

In order to realize a perpendicular exchange bias for applications, a robust and tunable exchange bias is required for spintronic applications. Here, we show the perpendicular exchange energy (PEE) in the TbxCo100−x/Cu/[Co/Pt]2 heterostructures. The structure consists of amorphous ferrimagnetic Tb–Co alloy films and ferromagnetic Co/Pt multilayers. The dependence of the PEE on the interlayer thickness of Cu and the composition of Tb–Co were analyzed. We demonstrate that the PEE can be controlled by changing the Cu interlayer thickness of 0.2 < tCu < 0.3 (nm). We found that PEE reaches a maximum value (σPw = 1 erg/cm2) at around x = 24%. We, therefore, realize the mechanism of PEE in the TbxCo100−x/Cu/[Co/Pt]2 heterostructures. We observe two competing mechanisms—one leading to an increase and the other to a decrease—which corresponds to the effect of Tb content on saturation magnetization and the coercivity of heterostructures. Sequentially, our findings show possibilities for both pinned layers in spintronics and memory device applications by producing large PEE and controlled PEE by Cu thickness, based on TbxCo100−x/Cu/[Co/Pt]2 heterostructures.

DOI： 10.3390/magnetochemistry7110141

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

In this paper, we demonstrate the magnetization-dependent inverse spin Hall effect (MD-ISHE) in TbxCo100-x/Pt/Y3Fe5O12 devices using the spin Seebeck effect. It was found that a thermally injected spin current is precessed around the magnetization of the TbxCo100-x alloy before it is converted into a charge current. Furthermore, the sign of the MD-ISHE voltage was found to depend on the Co magnetic moment direction, whereas the sign and magnitude of the conventional ISHE voltage are independent of the TbxCo100-x magnetization direction. Meanwhile, the spin rotation angle was estimated to be similar to 12% in TbxCo100-x/Pt. Our findings demonstrate that perpendicularly magnetized TbxCo100-x supplies additional symmetry to the ISHE and provides advantages in terms of tailoring the sign of the spin-current polarization through adjusting the alloy composition.

DOI： 10.1103/PhysRevB.103.214408

Publishing type：Research paper (scientific journal)   Publisher：Nature  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigates the effect of strain on the compensation temperature of ferrimagnetic Tb-Fe films formed on a flexible substrate. The compensation temperature is determined by the anomalous Hall measurement, and an application of 1.2% tensile strain reduces the compensation temperature by 12 K. X-ray magnetic circular dichroism reveals that approximately 5% of Fe magnetic moment and approximately 1% of Tb magnetic moment are reduced by an application of 0.9% tensile strain at the room temperature. To understand the greater reduction in Fe magnetization compared with that in Tb and the compensation temperature reduction simultaneously, a model applying molecular field theory is analyzed. Changes in three types of exchange coupling between Fe and Tb atoms are speculated to be caused by the strain.

DOI： 10.1038/s41598-021-85642-3

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：日本磁気学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Using samples of Co100-xTbx/Cu/Y3Fe5O12, we investigate the heat-to-charge current conversion phenomena in amorphous Co100-xTbx alloys. We find an enhancement of the inverse spin Hall voltage owing to the Tb impurity by means of the spin Seebeck effect. The spin Hall angle of Co68Tb32 is 3.5 times larger than that of Co, and mainly originates from the extrinsic spin Hall effect. Meanwhile, we detect an anomalous Nernst voltage owing to the magnetic properties of Co100-xTbx alloy. The sign of the inverse spin Hall voltage is observed to be the same for all Co100-xTbx samples, whereas the anomalous Nernst voltage changes its sign around the magnetization compensation composition. Our finding proves Co100-xTbx is an efficient spin-to-charge current convertor, and it has advantages for manipulating not only the inverse spin Hall effect but also the anomalous Nernst effect by means of adjusting the Tb concentration.

DOI： 10.1103/PhysRevApplied.14.064025

Publishing type：Research paper (scientific journal)   Publisher：AIP  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated the relation between the domain wall (DW) configuration and the strength of the interlayer exchange coupling (IEC) in multilayered magnetic wires, where a Ru spacer layer mediates the IEC between two ferromagnetic layers, and a Pt cap layer contributes to the interfacial Dzyaloshinskii-Moriya interaction. It was found that the antiferromagnetic IEC stabilizes the Neel-type DWs in the wires and that the stability varies with the strength of the antiferromagnetic IEC. The micromagnetic simulations imply that the Neel-type DWs are stabilized because the rotation of the magnetic moments in the DWs is restricted in the antiferromagnetically coupled ferromagnetic layers.

DOI： 10.1063/5.0013481

Publishing type：Research paper (scientific journal)   Publisher：Nature partner journal  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Spintronics is expected to be the basis for future ultra-low-energy nanoelectronic devices. To operate such devices at room temperature, amplifiers, batteries, capacitors, as well as spin current sources are required. Here we report a chalcogenide superlattice composed of GeTe and Sb2Te3 layers that have a topologically protected spin diffusion length exceeding 100 mu m at room temperature. A spin generator is demonstrated by combining magnetic injectors (TbFeCo) with this superlattice. The spin current was found to increase exponentially with the number of superlattice periods. We used this effect to demonstrate a 15-fold increase in the spin current. In addition, spin rectification is possible by growing the superlattice layers with atomic-level thickness accuracy. The reported chalcogenide superlattice spin generators and rectifiers open new opportunities to design low-energy spintronic integrated circuits and quantum computers.

File： 202007iPCM 2D.pdf

DOI： 10.1038/s41699-020-0157-8

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

File： FeNi long spin length_2020_Appl._Phys._Express_13_075503.pdf

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

File： fekuda tanabe GdFeCo STFMR.pdf

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

File： 202001_トピックス_粟野原稿_初校sawa.pdf

Publishing type：Research paper (scientific journal)   Publisher：Nature  

DOI： 10.1038/s41598-019-49567-2

Authorship：Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

File： ⑥224回研究会資料_鷲見聡先生.pdf

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

File： Aktar_2019_Appl._Phys._Express_12_053004.pdf

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Applied Physics  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：電気学会  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：電気学会  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

File： Kurokawa_2019_Jpn._J._Appl._Phys._58_030905.pdf

Publishing type：Research paper (scientific journal)   Publisher：Nature  

DOI： 10.1038/s41563-018-0236-9

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Publishing Group  

We have studied the magneto-optical spectra of ultrathin magnetic films deposited on Si substrates coated with an oxide layer (SiOx). We find that the Kerr rotation angle and the ellipticity of ~1 nm thick CoFeB thin films, almost transparent to visible light, show a strong dependence on the thickness of the SiOx layer. The Kerr signal from the 1 nm CoFeB thin film can be larger than that of ~100 nm thick CoFeB films for a given SiOx thickness and light wavelength. The enhancement of the Kerr signal occurs when optical interference takes place within the SiOx layer. Interestingly, under such resonance condition, the measured Kerr signal is in some cases larger than the estimation despite the good agreement of the measured and calculated reflection amplitude. We infer the discrepancy originates from interface states that are distinct from the bulk characteristics. These results show that optical interference effect can be utilized to study the magneto-optical properties of ultrathin films.

DOI： 10.1038/s41598-017-18794-w

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

File： 2019NatMat s41563-018-0236-9.pdf

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：電気学会  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Publishing type：Research paper (scientific journal)   Publisher：Crystals  

DOI： 10.3390/cryst8100377

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

File： 2018 Iemoto crystals-08-00377-v2 (4).pdf

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：電子情報通信学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

We have proposed an enhancement mechanism of the Hall effect, the signal of which is amplified due to the generation of a sustaining mode of spin current. Our analytic derivations of the Hall resistivity revealed the conditions indispensable for the observation of the effect: (i) the presence of the transverse component of an effective electric field due to spin splitting in chemical potential in addition to the longitudinal component
(ii) the simultaneous presence of holes and electrons each having approximately the same characteristics
(iii) spin-polarized current injection from magnetized electrodes
(iv) the boundary condition for the transverse current (J c, y = 0). The model proposed in this study was experimentally verified by using van der Pauw-type Hall devices consisting of the nonmagnetic bipolar conductor YH x (x ≃ 2) and TbFeCo electrodes. Replacing Au electrodes with TbFeCo electrodes alters the Hall resistivity from the ordinary Hall effect to the anomalous Hall-like effect with an enhancement factor of approximately 50 at 4 T. We interpreted the enhancement phenomenon in terms of the present model.

DOI： 10.7567/JJAP.57.033001

Authorship：Lead author,　Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Physics Soceity  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

We fabricated a Pt (3 nm)/Tb0.28Co0.72 (4 nm)/Ta (4 nm)/Tb0.26Co0.74 (4 nm)/Pt (3 nm) multilayered magnetic wire and investigated current-induced domain wall motion within it. We found that the Hall resistance of the Pt/Tb-Co/Ta/Tb-Co/Pt wire has four stable levels under a magnetic field of zero. Moreover, we observed that the domain walls in both the upper and lower ferromagnetic layers are controlled by a single current source. This indicates that Pt/Tb-Co/Ta/Tb-Co/Pt wire can be used in multi-level magnetic wire memory.

DOI： 10.1063/1.5017814

Publishing type：Research paper (scientific journal)   Publisher：Nature  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We demonstrate that the Faraday effect can be electrically and reversibly switched on and off at room temperature without changing the external magnetic field. A Co ultrathin film deposited on a Pt underlayer was used for the demonstration. An electric field was applied to the surface of the Co film by forming an electric double layer using an ionic liquid. The switching of the Faraday effect was caused by the electric-field-induced ferromagnetic phase transition in the system. The magnitude of the electrical change in the Faraday rotation angle and the ellipticity are also discussed. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/APEX.10.123201

Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：電気学会  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：電気学会  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We investigated the current-induced domain wall (DW) motion in Tb/Co multilayered wire with various substrate temperatures (T-s). The coercivity and DW propagation field of the Tb/Co multilayered film are 10 and 8 kOe, respectively. In the Tb/Co wire, the DW velocity is 2.4 m/s for a current density of 4.5x10(11) A/m(2) at room temperature. At T-s = 343 K, we also found that the DW velocity is about two times higher than that at room temperature. The enhancement of DW velocity can be attributed to thermally activated creep DW motion and/or the reduction of the depinning current density.

DOI： 10.1109/TMAG.2017.2676086

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated the current-induced domain wall motion (CIDWM) in Pt(3 nm)/TbxCo1-x(6 nm) alloy wires with various Tb composition (x). We found that the threshold current density (J(th)) for the CIDWM in the TbxCo1-x alloy wires decreases with increasing x. In particular, the J(th) with x = 0.37 is almost 3 times smaller than that with x = 0.23. We estimated Dzyaloshinskii-Moriya interaction (DMI) effective field (H-DMI) by measuring CIDWM in a longitudinal magnetic field. We found that DMI constant (D) estimated by the H-DMI also strongly depends on x. The size of the DMI may be modified by changing electronegativity or local atomic arrangement in Tb-Co alloy. These results suggest that Tb can induce strong H-DMI and effectively affect CIDWM in TbxCo1-x alloy wires. (C) 2017 Author(s).

DOI： 10.1063/1.4974280

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated the electric-current-induced dynamics of bubble domains in a perpendicularly magnetized ferrimagnetic {Tb/Co}(7) multilayer wire with a heavy-metal Pt cap layer. The {Tb/Co}(7) wire with the transition-metal-dominant and rare-earth-dominant magnetizations was obtained by changing temperature. We found that the bubble domains moved to the electric current direction with growing in oblique angles when electric current pulses were applied. The oblique directions of the bubble-domain's growth in the {Tb/Co}(7) wire with the transition-metal-dominant and rare-earth-dominant magnetizations were opposite with each other. The micromagnetic simulations imply that these oblique growths are accounted by the spin injection from the Pt layer via the spin Hall effect. (C) 2017 Author(s).

DOI： 10.1063/1.4974067

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated the current-induced domain wall motion (CIDWM) in Pt (3 nm)/Tb0.34Co0.66 (6 nm) alloy wire at various temperatures (T). The threshold current density (Jth) for the CIDWM in the Tb-Co alloy wire was 0.85 x 10(11) A/m(2) at room temperature, and drastically decreased as T was increased. Particularly, at T = 343 K, Jth (= 0.13 x 10(11) A/m(2)) was almost 7 times lower than that at room temperature. The reduction in Jth can be attributed to thermally activated creep motion and a reduction in the depinning current density. These results indicate that devices using CIDWM can be thermally assisted. (C) 2017 Author(s).

DOI： 10.1063/1.4979727

Authorship：Last author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：電気学会  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：電子情報通信学会  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Nanoimprint lithography (NIL) is an effective method to fabricate nanowire because it does not need expensive systems and this process is easier than conventional processes. In this letter, we report the Current Induced Magnetization Switching (CIMS) in perpendicularly magnetized Tb-Co alloy nanowire fabricated by NIL. The CIMS in Tb-Co alloy wire was observed by using current pulse under in-plane external magnetic field (H-L). We successfully observed the CIMS in Tb-Co wire fabricated by NIL. Additionally, we found that the critical current density (J(c)) for the CIMS in the Tb-Co wire fabricated by NIL is 4 times smaller than that fabricated by conventional lift-off process under H-L = 200Oe. These results indicate that the NIL is effective method for the CIMS. (C) 2017 Author(s).

DOI： 10.1063/1.4977769

Publishing type：Research paper (scientific journal)   Publisher：IEEE  

DOI： 10.10631/1.4974067

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：一般社団法人 日本物理学会  

<p>正孔と電子とが同等なキャリヤ特性を有する非磁性両極性伝導体では、（１）適当な外部磁場および電流・スピン流境界条件の下で、スピン流モードのみが自律的に発生し、（２）それがホール効果の強さを共鳴的に増強することを理論的に説明し、（３）両極性伝導体YH_2_およびScH_2_を用いた実験結果と比較する。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_1263

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.72.2.0_816

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：一般社団法人 日本物理学会  

<p>プラチナ層と接する垂直磁化フェリ磁性体多層膜Tb/Coの{Tb/Co}_7_/Pt細線上にバブル磁区を生成し，電流印加による挙動を調べた．電流印加によりバブル磁区は細線の端方向への傾斜をもって成長した．フェリ磁性体の磁化の主体となる原子がTbとCoの場合で傾斜方向が逆になることがわかった．プラチナ層からのスピンホール効果を考慮したマイクロマグネティスシミュレーションでも同様の結果が得られ，このバブル磁区の傾斜はスピンホール効果によって説明できることがわかった</p>

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigated the current-induced domain wall motion (CIDWM) in Pt/GdFeCo bilayer wires where the thicknesses of the GdFeCo layer are 110 and 150 nm. We found that the direction of CIDWM in the Pt/GdFeCo wires is the same as the current flow direction. The velocity of the domain wall depends on the in-plane magnetic field. These results indicate that the CIDWM along the current direction in the Pt/GdFeCo wires is probably attributed to the spin Hall effect and Dzyaloshinsky-Moriya interaction. Generally, these effects do not appear in thick magnetic wires because they effectively occur at the interfaces of a heavy metal and magnetic layers. Therefore, these results are interesting phenomena because they probably suggest that the spin Hall effect and Dzyaloshinsky-Moriya interaction in the Pt/GdFeCo wire have an anomalously long-range influence. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.07MC02

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：映像情報メディア学会  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

© 2016 Author(s). In this report, we studied the temperature dependence of magneto-optical Kerr rotation in [(GeTe)2/(Sb2Te3)1]n=8 topological superlattice from room temperature to 440 K. At temperatures lower than a threshold temperature of 360 K, the Kerr signal was negligible. On the other hand, at temperatures higher than the threshold, two resonant Kerr peaks with a mirror-symmetry for one field scan from + 20 to - 20 kOe were observed. We found that the resonant field of each Kerr signal peak is gradually decreased with increasing the temperature, while its magnitude is increased. We further found that a phase transition from the high temperature phase to a low temperature phase can be controlled by an external magnetic field.

DOI： 10.1063/1.4943152

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

© 2016, The Minerals, Metals & Materials Society. We studied the magnetic field dependence of magneto-optical Kerr rotation of the [(GeTe)2/(Sb2Te3)1]8 topological superlattice at different temperatures (from 300 K to 440 K). At low temperatures (less than 360 K), the Kerr signal was within noise level. However, large Kerr rotation peaks with a mirror symmetric loop were at high temperatures (higher than 360 K). The temperature dependence of the observed Kerr signal can be attributed to the breaking of spatial inversion symmetry, which induces a narrow gap in surface state bands due to the Ge atomic layer movement-induced phase transition in the superlattice. We found that the resonant field of each Kerr peak gradually decreases with increasing temperature. On the other hand, the phase transition from a high temperature phase to a low temperature one could be controlled by external magnetic fields.

DOI： 10.1007/s11664-016-4389-5

Publishing type：Research paper (scientific journal)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In this study, the strain-induced change in the magnetic anisotropy of perpendicularly magnetized thin metals (TbFeCo and Pt/Co/Pt) deposited on a polyethylene naphthalate flexible substrate was investigated. The in-plane uniaxial tensile strain was reversibly applied up to 2%. The magnetic anisotropy was reversibly changed in both samples with applied stress. In the TbFeCo film, a marked change in magnetic anisotropy energy of 1.2 x 10(5) J/m(3) was observed. In the Pt/Co/Pt film, where the thickness of Co was 2-4 monolayers, the stress-induced changes in interface and volume contributions to magnetic anisotropy were individually determined. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/APEX.9.043004

Publishing type：Research paper (scientific journal)   Publisher：Applied Physics Express  

Authorship：Last author   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jsamd.2016.03.001

Publishing type：Research paper (scientific journal)   Publisher：AIP  

Publishing type：Research paper (scientific journal)  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_1170

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：一般社団法人 日本機械学会  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_1156

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

The current-induced domain wall motion (CIDM) in thin perpendicular magnetized ferromagnetic wires sandwiched between a heavy metal and an oxide has been expected to be very efficient in getting high DW velocity at low current density for developing spintronic devices [1-3]. The addressed high velocity in these asymmetric wires is attributed to the presence of structural inversion asymmetry (SIA) and/or heavy metals like Pt which can lead to strong spin-orbit interaction (SOI) and induce additional spin-orbit torques (SOTs). Recently, a transition from bulk to interfa-cial effect is confirmed as a change in the DW motion direction at a reduced layer thickness of Co/ Ni multilayer down to 2.1 nm [4]. As discussed in Ref. [4], the adiabatic spin-transfer torque (STT) dominates the DW motion in the thick regime, while the interfacial torque due to the spin Hall effect (SHE) induces DW motion in the thin regime. In an earlier study [5], however, we can still observe the SOTs-induced DW motion up to a thickness of ∼ 10 nm for the asymmetric interfacial wire with the layered structure of SiO&lt
inf&gt
2&lt
/inf&gt
/[Tb(3.2 Å)/Co(2.6 Å)]&lt
inf&gt
n&lt
/inf&gt
/Pt(20 Å). The high efficiency of SOTs in our wires can be explained by an addition of the extrinsic SHE from Co ultrathin layers due to Tb rare-earth impurity-induced skew scattering in the Co layer with the aid of SOI [6,7]. In this study, we present the current-induced DW motion in the Tb/Co wires with different layered structures. The extrinsic SHE is tuned by changing the thickness of Co ultrathin layers, number of Tb/Co interfaces, and formation of Tb-Co alloy magnetic layer.

DOI： 10.1109/INTMAG.2015.7157554

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigated the bubble-domain dynamics in TbFeCo wires with perpendicular magnetization under electric current flows. In TbFeCo wires with relatively low saturation magnetization (M-s), the current pulse caused the bubble domains to collapse without moving. In TbFeCo wires with relatively high M-s, however, the bubble domains grew in the current direction. We explain these shape changes by assessing the M-s-dependent forces caused by the exchange field and magnetostatic field. We also found that we could control the current-induced behaviors of the bubble domains by using an external magnetic field. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/APEX.8.073002

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Applied Physics Express  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Current driven magnetic domain wall (DW) motions of fern-magnetic TbFeCo wires have been investigated. In the case of a Si substrate, the critical current density (Jc) of DW motion was successfully reduced to 3 x 10(6) A/cm(2). Moreover, by using a polycarbonate (PC) substrate with a molding groove of 600 nm width, the Jc was decreased to 6 x 10(5) A/cm(2). In order to fabricate a logic in memory, a current driven spin logics (AND, OR, NOT) have been proposed and successfully demonstrated under the condition of low Jc. These results indicate that TbFeCo nanowire is an excellent candidate for next generation power saving memory and logic. (C) 2015 The Author. Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2014.12.081

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated current-induced DW motion in asymmetric interfacial multilayered Tb/Co wires for various thicknesses of magnetic and Pt-capping layers. It is found that the driving mechanism for the DW motion changes from interfacial to bulk effects at much thick magnetic layer (up to 19.8 nm). In thin wires, linearly depinning field dependence of critical current density and in-plane field dependence of DW velocity suggest that the extrinsic pinning governs field-induced DW motion and injecting current can be regarded as an effective field. It is expected that the high efficiency of spin-orbit torques in thick magnetic multilayers would have important implication for future spintronic devices based on in-plane current induced-DW motion or switching. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4916819

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：一般社団法人電子情報通信学会  

At room temperature, the iPCM shows high conductivity RESET phase and does not show any magneto-optical Polar Kerr signal, because it is made by non-magnetic materials. However, when the temperature is over 420K which corresponding to low conductivity SET phase, it shows very large Kerr rotation angle of 0.3 degree which is almost same value of TbFeCo MO standard recording layer. Moreover, surprisingly, the Kerr hysteresis loop shows mirror symmetry. This is the first discovery in MO effect.

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：一般財団法人電子情報通信学会  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：応用物理学会  

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：映像情報メディア学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have carried out magnetotransport measurements of the bipolar conductor YHx (x similar or equal to 2) employing the ferromagnetic conductor Co as the source and drain electrodes, from which the spin-polarized currents are injected. Both the Hall resistivity (HR) and transverse magnetoresistivity (TMR) ratio are enhanced by a factor of similar to 3 and similar to 6, respectively, when Co electrodes are used instead of Au electrodes. We derived two types of closed formulae of HR and TMR, the first (second) type of which was derived by simultaneously (independently) considering the external magnetic field and spin-orbit interaction, but both types of which were derived by considering spin-dependent electrochemical potential caused by the presence of the ferromagnetic electrodes. Carrier parameter assessments based on the two types of formulae as well as the two types of electrode samples enable us to infer that coupling mechanisms between the external magnetic field and spin-orbit interaction are required for the precise interpretation of HR and TMR measured in the simultaneous presence of magnetic field and spin splitting in a diffusion force field, especially for conductors with strong spin-orbit interaction. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.013001

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics  

We have carried out magnetotransport measurements of the bipolar conductor YH<inf>x</inf>([Formula: see text]) employing the ferromagnetic conductor Co as the source and drain electrodes, from which the spin-polarized currents are injected. Both the Hall resistivity (HR) and transverse magnetoresistivity (TMR) ratio are enhanced by a factor of ∼3 and ∼6, respectively, when Co electrodes are used instead of Au electrodes. We derived two types of closed formulae of HR and TMR, the first (second) type of which was derived by simultaneously (independently) considering the external magnetic field and spin–orbit interaction, but both types of which were derived by considering spin-dependent electrochemical potential caused by the presence of the ferromagnetic electrodes. Carrier parameter assessments based on the two types of formulae as well as the two types of electrode samples enable us to infer that coupling mechanisms between the external magnetic field and spin–orbit interaction are required for the precise interpretation of HR and TMR measured in the simultaneous presence of magnetic field and spin splitting in a diffusion force field, especially for conductors with strong spin–orbit interaction.

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We have studied the field- and current-induced domain wall (DW) motion in perpendicularly magnetized Tb/Co multilayer wires with asymmetric interface structures. We found that both up/down and down/up walls of a domain move at the same velocity. In the current-induced case, the DWs were moved along the current flow, not electron flow. This can be attributed to spin-orbit torques induced by structural inversion asymmetry (SIA). In addition, the DW velocity was changed by inserting ultrathin Pt interlayers into the wire stack. These results suggest that the SIA of the wire is tunable by changing layered structures.

DOI： 10.1109/TMAG.2014.2328654

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：応用物理学会  

Publishing type：Research paper (international conference proceedings)   Publisher：European Phase Change and Ovonics Symposium  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Interfacial phase change memory (iPCM), that has a structure of a superlattice made of alternating atomically thin GeTe and Sb2Te3 layers, has recently attracted attention not only due to its superior performance compared to the alloy of the same average composition in terms of energy consumption but also due to its strong response to an external magnetic field (giant magnetoresistance) that has been speculated to arise from switching between topological insulator (RESET) and normal insulator (SET) phases. Here we report magneto-optical Kerr rotation loops in the visible range, that have mirror symmetric resonances with respect to the magnetic field polarity at temperatures above 380 K when the material is in the SET phase that has Kramers-pairs in spin-split bands. We further found that this threshold temperature may be controlled if the sample was cooled in a magnetic field. The observed results open new possibilities for use of iPCM beyond phase-change memory applications.

DOI： 10.1038/srep05727

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人　電子情報通信学会  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人　電子情報通信学会  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：映像情報メディア学会  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have investigated domain wall (DW) motion in Tb/Co multilayer wires with a large DW depinning field similar to 3.0 kOe and different wire widths. In this system, the DW depinning field was decreased as a linear dependence of injecting current. A high effective efficiency epsilon similar to 5 x 10(-13) T m(2) A(-1) was obtained. Threshold current density for the DW motion was found to be approximately 3 x 10(11) A/m(2) for the wires. High DW velocity up to 90 m/s was observed. In addition, the DW velocity showed a strong dependence on perpendicular (easy-axis) magnetic field. These results suggest that the Tb/Co wire is an excellent candidate for the high-speed and stability of stored information in DW-controlled devices. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4868918

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：映像情報メディア学会  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：日本磁気学会  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本応用磁気学会  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Current-induced domain wall (DW) motion has been investigated in interfacial asymmetric SiO2/TbFeCo/Pt wires with different wire widths and thicknesses. The reversed DW motion was observed in these interfacial asymmetric wires at zero field and room temperature. This reversal of DW motion was attributed to the structural inversion asymmetry-induced spin-orbit torques (SOTs) from the Pt/TbFeCo interface and Pt layer of the wire. We found that the reversed DW velocity strongly depends on the size of wires, typically large for thin and narrow wires, suggesting that the SOTs effectively enhance the reversed DW velocity in these asymmetric TbFeCo wires. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.123001

Authorship：Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We studied the motion of magnetic domain walls (DWs) in SiO2/TbFeCo/Pt (asymmetric) and Pt/TbFeCo/Pt (symmetric) nanowires. The reversed DW motion was observed in the asymmetric wire at zero field and room temperature. The reversed DW motion was attributed to the structural inversion asymmetry-induced spin-orbit torques from Pt/TbFeCo interface and Pt layer of the asymmetric wire. The DW velocity sign was again reversed when the current density is larger than 1.52 x 10(11) A/m(2) which corresponds to threshold of Walker-breakdown current density.

DOI： 10.1109/TMAG.2013.2252003

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

We studied the domain-wall (DW)-induced magnetoresistance (MR) effect in TbFeCo wires with a thickness of 18 nm and different widths at room temperature. In wide (up to 10-μm-width) wires, small MR values that weakly depended on the number of DWs inside the wires, were obtained. This could be attributed to multi-domain structures that reduced the spin asymmetry in the wire. For all wires, the MR values strongly depended on the bias current. In a narrow (0.8-μm-width) wire with a single DW structure, large MR values of up to 8% were observed at a low bias current and depended on the DW structure inside the TbFeCo wires. On the other hand, the MR values were greatly reduced at large bias currents, which induced magnon and phonon scattering effects. The contribution of the single DW resistivity to the MR effect was found to be large for a narrow wire due to the large spin asymmetry of conduction electrons through the DWs. The well-defined and controllable number of DWs inside magnetic wires is expected to obtain high and multi-level MR values as well as high potentials for future magnetic devices. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.62.1933

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：一般社団法人電子情報通信学会  

Warning that a shortage of storage as well as water and electricity by the rapid economic growth of emerging countries has been sounded. Even If someone increases the production of a lot of storage devices to solve this problem, they can not be used because of shortage of electric power. In order to solve the problem, a new storage device named as solid state magnetic memory(low power consumption and huge data capacity)should be studied In this presentation, we will report about a basic study of CoB/Ni magnetic nanowire memory as a one solution.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：映像情報メディア学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We have theoretically studied a methodology for the measurement of the degree of spin polarization (P) in metals as well as semiconductors. Our principle is based on the correlation existing between transverse resistivity (rho(yx)) and longitudinal resistivity (rho(xx)), both influenced by transverse scattering due to a spin-orbit interaction (SOI) as well as longitudinal scattering due to usual mechanisms. Our spin polarization analyzer employs an unknown polarization conductor as a source electrode from which spin-polarized electrons are injected into a nonmagnetic (NM) channel region. The channel length is set to be much smaller than its spin diffusion length so that rho(yx) and rho(xx) in the NM region, both complementarily influenced by carrier spin polarization, would be measured to obtain the P value. Also, application to OR and XOR logic gates are discussed on the basis of our spin polarization analyzer. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.013004

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Current-induced domain wall motion has been investigated in perpendicular magnetic anisotropy SiO2/TbFeCo/Pt ( asymmetric interface) and Pt/TbFeCo/Pt (symmetric interface) wires. The domain wall is found to be moved in opposite to the electron-flow direction in the asymmetric interface wire whereas it is kept same direction in the symmetric one at room temperature. As an alternative to the conventional spin-transfer torque, the Rashba field at the TbFeCo/Pt interface and the spin Hall current injected from the Pt layer are possibilities of the reversed domain wall motion in an ultrathin magnetic film sandwiched by dissimilar materials. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/APEX.5.125201

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：International Union of Pure and Applied Physics  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The spin-transfer torque motion of magnetic domain walls (DWs) in a CoB/Ni-based nanowire driven by a low current density of (1.12 +/- 0.8) x 10(11) Am-2 has been observed indirectly by magnetotransport measurements. A high DW velocity of 85 +/- 4 m/s at zero field was measured at the threshold current density. Upon increasing the current density to 2.6 x 10(11) Am-2, the DW velocity increases to 197 +/- 16 m/s before decreasing quickly in the high-current-density regime attributed to nonadiabatic spin-transfer torque at a low damping factor and weak pinning. The addition of B atoms to the Co layers decreased the magnitude of saturation magnetization, Gilbert damping factor, and density of pinning sites, making the CoB/Ni multilayer nanowire favorable for practical applications. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.093002

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：American Institute of Physics  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We demonstrate the possibility to write and modulate the magnetic domain walls in a TbFeCo single layer nanowire (300 nm width, 150 mu m length). To realize this, a tiny magnetic domain was nucleated by an Oersted field produced by a 1.6 MHz pulse current (35 mA in amplitude, 5-40 ns in length) crossed the wire. To write the wall to the wire, a DC current was used to drive the nucleated domain (with two walls in two sides) to the wire in accordance with spin-transfer torque mechanism. A critical current density of J(c) = 3.5 x 10(10) Am-2 was required to control the motion of the walls in the wire. It was found that the size of the domain moving in the wire could be adjusted by either external field or the length of the nucleated pulse current. This could be considered as an important note for writing process in domain wall spin-torque devices, especially, memory elements. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704395]

DOI： 10.1063/1.4704395

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：一般社団法人電子情報通信学会  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

We present here a study of exploiting Lorentz transmission electron microscopy to observe the magnetic structure in a nanobridge formed by confining a magnetic domain wall. The domain wall is nucleated in an elliptical pad by magnetization reversal and is driven to be pinned at the constriction to form a complex magnetic structure. High-resolution Lorentz microscopy shows that such a structure is composed by a mixture of S and C states of smooth rotation of the magnetization through the nanobridge rather than a conventional single wall as observed previously. This confinement contributes a domain wall resistance observed via anisotropic magnetoresistance presented previously. A serial transformation from S state to S/C mixture, to C state and finally to S state of the topology of the flux is evidently confirmed. © 2011 IEEE.

DOI： 10.1109/TMAG.2011.2156395

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

The motion of magnetic domain walls (DWs) in TbFeCo wires induced by low-current density up to 4.97 x 10(10) A/m(2) has been directly observed by Kerr polarized optical microscopy. The critical current density slightly increases with wire width, from 4.97 x 10(10) A/m(2) for 800-nm-width wires to 6.16 x 10(10) A/m(2) for 1500-nm-width wires. DW velocity is estimated to be 28 +/- 2 m/s, and mostly independent on the wire width. Increasing current density results in an increase of the wall velocity up to 59 +/- 4 m/s. These findings indicate that TbFeCo nanowire is an excellent candidate for low-energy, fast accessing DW-controlled devices. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/APEX.4.093002

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Journal of Physics  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

In nanoparticulate films with perpendicular magnetic anisotropy, a large demagnetizing field almost compensates for the experimentally designed change in the magnetic field applied parallel to the film normal. We propose a new method based on field-cycling to eliminate the uncertainty in the demagnetizing response from the analysis of the activation volume of the reversal or magnetic activation moment in such films. In this method, the applied field induced variation in the magnetic relaxation rate is measured before the effect of the demagnetizing field becomes dominant. We also discuss an analogical thermal-cycling method to clarify the temperature dependence of the barrier height for magnetization reversal in a magnetic field. We apply these methods to a Co74Pt16Cr10-SiO2 nanoparticulate film as an example. The results demonstrate that these methods are useful for studying thermal fluctuations in perpendicular recording media. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/266/1/012059

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the 22nd Symposium on Phase Change Optical Information  

Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Magnetics Society of Japan  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOCIETY APPLIED PHYSICS  

A stacked volumetric optical disks (SVOD) system has been developed to achieve an over 1 Tbytes cartridge capacity using a commercialized drive and conventional recording layers. To confirm the reliability of thin optical disks in SVOD, several feasibility tests were conducted. The recording power margin, tilt margin and read stability of the thin optical disks were measured, and the lifetime of the thin optical disks was estimated. The results were similar to those of conventional 1.2-mm-thick optical disks regardless of the disk thickness.

DOI： 10.1143/JJAP.47.5812

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have studied the perpendicular magnetic anisotropy of Co/Pd multilayers for ultrahigh recording density patterned media. By using Pt as an underlayer, the magnetic anisotropy enhances significantly, which is considered to be due to a magnetostriction by inducing a tensile strain into the Co/Pd multilayers. A patterned medium using the Co/Pd multilayers has been successfully fabricated with the diameter of the dots and the distance between the center of the dots measuring 20 and 30 nm, respectively. The coercivity of the nanopatterned medium is 9.5 kOe. (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2831331

Authorship：Lead author   Language：Japanese   Publishing type：Part of collection (book)   Publisher：日経BP社  

日立マクセルと日立製作所は，大量のデータを長期保存する（アーカイブ）用途に向けて，1カートリッジの記録容量が2.4Tバイトなどと大きい光ディスク媒体「SVOD」と専用の記録再生装置などを開発した。薄型化したBlu-ray Disc媒体を1カートリッジに数十枚収めることで実現している。既存のファイル管理ソフトを使えば，あたかも2.4Tバイトの光ディスクとして扱えるという。

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 レーザー学会  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Magnetic domain nucleation site distributions within a perpendicular magnetic film were measured by magnetically confining nucleated domains within small regions in the film. The confinement was achieved by placing a high coercivity layer adjacent to the layer under test and using the stray fields from domains recorded in this layer to magnetostatically halt domain wall motion in the test layer. Experimental results confirm the functionality of this method, and are shown for two samples with different magnetic properties. © 2005 IEEE.

DOI： 10.1109/TMAG.2005.854876

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

This article presents a theoretical model for the temperature dependent magnetic properties for a Co/Pd multilayer thin film medium assuming virtual interface (VIF). We assume that the exchange integral for the Co-VIF interaction is 1.38 times the exchange integral for the Co-Co interaction. Based on the mean field theory, temperature dependences of the average Co spin, the virtual interface spin, saturation magnetization Ms and exchange stiffness constant A are presented for the [Co(0.2 nm)/Pd(0.8 nm)](12) multilayer thin film. Fairly good agreement in Ms between the simulations and the experiments suggests validity in the temperature dependence of A. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.1849671

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 レーザー学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The Magnetics Society of Japan (MSJ)  

To eliminate the time required for test data recording before test read, we studied test read approaches using as-deposited MAMMOS media, i.e., without recording the pre-determined test data onto the media. We consider the accumulation of the absolute values of this difference in the two moving averages as a good criterion to obtain desirable readout laser power. The results from our experiments suggest the proposed method is effective as long as the as-deposited conditions can be well-controlled.

DOI： 10.3379/tmjpn2001.4.156

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan (MSJ)  

With consideration to the Curie-Weiss law, we investigate magnetization reversal beyond the Curie temperature, from theoretical to experimental. This paper outlines a theoretical model in accordance with the Curie-Weiss law and also presents a new criterion for the shape stability of recorded domains using magneto-optical recording or hybrid recording. Fairly good agreement was obtained between the theoretical and experimental investigations.

DOI： 10.3379/tmjpn2001.4.186

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

We present results of a time-resolved study of the ultrafast magnetic response of Gd23.1 Fe71.9 Co5.0 magnetically amplified magnetooptical systems (MAMMOS) structures under conditions near actual read/write temperatures. An all-optical pump and probe method was used in which an intense (pump) light beam excited a medium due to ultrafast laser heating and a less intense (probe) beam monitored this photo-excited state through the magnetooptical Kerr effect. Our experiment clearly demonstrates that the photo-excitation effectively excites coherent spin waves in the magnetic material. Precession frequencies of several gigahertz and relaxation times in the nanosecond range were observed.

DOI： 10.1109/TMAG.2004.834201

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：公益社団法人 日本磁気学会  

This paper describes results of a time-resolved study of the ultrafast magnetic response of Gd<sub>23.1</sub>Fe<sub>71.9</sub>Co<sub>5.0</sub> MAMMOS structures under conditions near actual read temperature. An all-optical pump and probe method was used, in which an intense (pump) light beam excited a medium due to ultrafast laser heating and a less intense (probe) beam monitored this photo-excited state through the magnetooptical Kerr effect. Our experiment clearly demonstrates that the photo-excitation effectively excites coherent spin waves in the magnetic material. Precession frequencies of several GHz and relaxation times in the nanosecond range were observed.

DOI： 10.3379/jmsjmag.28.318

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

The concept of a low cost, single layer read only memory (ROM) compatible with the magnetic amplifying magneto-optical system (MAMMOS) is introduced. This ROM technology relies on the creation of nucleation sites in the medium for information storage and read back. Several methods of implementing the MAMMOS ROM are proposed and the distribution of nucleation sites is experimentally investigated to gain a better understanding of how to control these sites.

DOI： 10.1117/12.556950

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：応用物理学会  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

We present results of first-surface blue zero-field magnetic amplifying magneto-optical system (MAMMOS) recording of isolated marks of 60 nm and a single tone carrier of 90 nm. The signals are recorded by laser-pulsed magnetic field modulation using a blue laser, a recording head with numerical aperture (NA) = 0.7 with integrated thin film coil and a free working distance of 12 mum from the disc. The media are covered with a 3 mum thin cover layer to prevent heating induced contamination of the optics.

DOI： 10.1143/JJAP.42.1078

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan (MSJ)  

In the ongoing effort to achieve ultra high density Magneto-Optical recording, Laser Pumped Magnetic Field Modulation (LP-MFM) and Magnetic Amplifying Magneto-Optical System (MAMMOS) are considered promising methods. Using LP-MFM, crescent domains are recorded in a recording layer. Micro-magnetic simulations for the MAMMOS readout have already been reported assuming a crescent domain and red laser irradiation. Huth's equation simulations for the MAMMOS readout have also been reported assuming a circular recorded domain and blue laser irradiation. Micro-magnetic simulations for the MAMMOS readout assuming a blue laser irradiation, however, have not so far been reported. This paper presents the analysis of the combination of a 405nm blue laser and the MAMMOS readout from crescent recorded domains using the micro-magnetic simulations. In this work, MAMMOS readout from a crescent recorded domain is shown to be possible even with blue laser irradiation.

DOI： 10.3379/tmjpn2001.2.297

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan (MSJ)  

For almost all optical disks, signal decline is mainly due to inter symbol interference (ISI) caused by laser beam spot size or magnetic aperture size. Such 151 does not appear for Zero Field Magnetic Amplifying Magneto-optical System (Zero Field MAMMOS). The limit of the frequency response comes from the frequency range of the MO readout channel. MAMMOS has a resolution for 1/10 of a laser beam corresponding to 0.1μm. Decrease in the carrier level and error of less than 0.1μm is caused by expansion failure. If expansion failure were circumvented, Zero Field MAMMOS would have a possibility of readout with 0.04μm resolution using a laser with wavelength, 650nm and an objective lens of NA, 0.6.

DOI： 10.3379/tmjpn2001.2.294

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Experiments show that the laser power margin for correct MAMMOS readout of small, packed domains becomes very small. In order to study this, a model is presented for the MAMMOS readout process. This model, supported by numerical simulations, explains the experiments and shows good agreement to the experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本応用磁気学会  

A new type of magnetic amplifying MO system (MAMMOS) named as Zero-Field MAMMOS was developed. Unlike the standard MAMMOS, its domain expansion scheme does not require the use of any external magnetic field. Although the MO signal enhancement ratio of the Zero-Field MAMMOS is small compared with that of the standard MAMMOS, it is possible to realize twice the higher density of DVD with a wide system margin, even under the same optical conditions as for DVD (650 nm laser and NA 0.60 objective lens). It was also confirmed that bit error rate for 4.5 times larger density recording was still lower than 1e10^<-4>.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

We investigated very high-density recording performance of the zero-field magnetic amplifying magnetooptical system (MAMMOS) with a 635 nm laser diode and a 0.60 N.A. objective lens. It was shown that the linear bit length of 0.13 mum was successfully reproduced with sufficient readout margins. The recording density up to 7.1 Gbit/in(2) was demonstrated by combining the zero-field (ZF)-MAMMOS with an in-groove disk structure.

DOI： 10.1143/JJAP.41.1654

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Ultrafast 100 femtosecond laser light was irradiated on an amorphous GdFeCo film under a DC magnetic field. Complete magnetization reversal and rewritable response were observed in a less than 1 picosecond time period. This experiment reveals the intrinsic capability of ultrafast high-speed rewitable storage under the thermomagnetic switching scheme. Current pure magnetic recording such as that in the case of hard disk storage has a serious spin reversal time problem limited by the ferromagnetic resonance (FMR) frequency. Such frequency is ordinarily 1 to 3 GHz, which means that the recording speed limit is of a similar order. A one-picosecond response enables a very attractive future information storage scheme realizing 10 to 1000 Gbps ultrafast devices.

DOI： 10.1143/JJAP.41.1650

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Pump-pulse induced magnetization reversal of amorphous Gd23.1Fe71.9Co5.0 showed a subpicosecond magnetization collapse followed by a slower reversal. The reversal dynamics is well described by the Bloch equation via a reversal time that does not depend on temperature, but strongly decreases with increasing pump fluence. A comparison to data obtained in external saturation field and in remanence opened the way to separate the contributions due to temperature induced effects within single domains from those related to field induced domain formation.

DOI： 10.1103/PhysRevB.65.012413

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Hybrid recording has already been realized in laser beam assisted perpendicular magnetic recording in audio recordable MiniDiscs. In the year 2000 alone, more than 20 million drives and 220 million disks were shipped. Hybrid recording is expected to be a very strong candidate in the near future in the very high density region, exceeding terabits/in2. Here, we report on hybrid recording with the capability to overcome two of the main serious problems
the paramagnetic limit in high density region and the writing speed limit caused by ferromagnetic resonance around 2 to 5 GHz.

DOI： 10.1109/INTMAG.2002.1001397

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (conference, symposium, etc.)   Publisher：IEEE  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In a magnetic amplifying magnetooptical system (MAMMOS) disk, the copying process of a magnetic domain from the recording layer into the readout layer is investigated by using a laser spot diameter of 0.66 mum. Interference between neighboring bits occurs when the spatial resolution of the copy process Is larger than half the domain size. It is observed that a reduction of the readout power from 2.3 to 2.0 mW corresponds to a decrease of the copy window from 0.5 to 0.06 mum. As a result, at 2.0 mW packed magnetic domains with a width of only 0.11 mum have been resolved without interference by using domain expansion.

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：一般社団法人電子情報通信学会  

光学分解能を超えた高密度な記録磁区を大きな信号で再生する一手法として, 磁区拡大再生技術がある.これは, 記録層に記録された記録磁区に再生レーザ光を照射して, 再生層に転写及び拡大させる技術で, 極めて大きな信号振幅で再生できる.本論文では磁区拡大再生技術に関して, 背景となった技術も含めて解説する.論文中では, まず高密度な光磁気記録を可能とするための光学系を検討した後, 光パルス磁界変調方式が望ましいことを説明する。次に光学分解能を超えた再生技術として磁気超解像について延べる.その後, 磁区拡大再生技術に関して, 最近の研究成果も加えながら原理を説明し, これからの高密度光磁気記録に関して延べる.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

Femtosecond laser pulse induced magnetization reversal of α-Gd_23.1Fe_71.9Co_5.0 was investigated by time-resolved measurements of the polar Kerr-rotation. The dynamics is found to follow the Bloch-equation via a relaxation time that does not depend on temperature but strongly decreases with increasing excitation density. A minimum value of (190±40)ps was obtained for the highest applicable pump-fluence. Comparing the reversal dynamics to temperature induced variations of magnetization within a single domain state and to the magnetization dynamics measured in remanence, the different contributions of transient temperature and domain formation to the magnetic response are separated.

DOI： 10.3379/jmsjmag.25.202

Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10465307

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

The combination of Magnetic Amplifying Magneto-Optical System (MAMMOS) media, a blue laser and a high NA objective lens has been investigated using simulations and experiments. This paper describes the experimental and simulated results of domain copying phenomena for the MAMMOS media using a 413nm blue laser and an objective lens with a numerical aperture (NA) of 0.9. Without an external magnetic field, the readout laser was irradiated onto the MAMMOS media. Since the phenomena were related to Rear Aperture Detection phenomena, the signal amplitude simulation assumed temperature dependence of the Kerr rotation, the aperture thermal properties and the Gaussian laser beam profile. This paper also presents the analysis of expansive and shrinking forces per unit wall area concerning the MAMMOS readout using the blue laser and the high NA objective lens.

DOI： 10.3379/jmsjmag.25.359

Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10465344

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：応用物理学会分科会日本光学会  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Very small domains are recorded on the MAMMOS disk and they can be detected using RF readout field. The MO signal amplitude of 20 nm domains ran be enhanced to the saturated signal level. For these small domains, the thermal stability problem is investigated, Even if high laser power for readout is irradiated to the small domains, the reproduced sihnal was maintained. The result indicates that the recording layer of TbFeCo possesses an advantage for para-magnetic limit problem over 100 Gbits/in(2).

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

MAMMOS (Magnetic Amplifying Magneto-Optical System) is a technology for reproducing a large signal during MO readout from a small magnetic domain. It has hitherto been considered that the domain recorded on the recording layer is copied to and expanded on the readout layer by irradiating the readout layer with a laser beam and applying a perpendicular magnetic field. However, we discovered that it is very effective for readout of small magnetic domains to apply an in-plane magnetic field. Under conditions where λ = 635 nm and NA = 0.55, the bit error rate (BER) of 0.15μm packed domains was improved to 2×10<sup>-4</sup>, while the BER of 0.2 μm packed domains was 2 × 10<sup>-4</sup> when an in-plane magnetic field was not applied.

DOI： 10.3379/jmsjmag.24.395

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：一般社団法人電子情報通信学会  

MAMMOS(Magnetic Amplifying Magneto-Optical System)is one of the technologies that can overcome the diffraction limit. Since, it can achieve both high resolution and large signal simultaneous1y, it is available for next generation MO systems. We discovered that it is very effective for readout of small magnetic domains to apply an in-plane magnetic field. Under conditions where λ=635 nm and NA=0.55, the bit error rate(BER)of 0.15 μm packed domain was 2×10^<-4>.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

Read/write characteristics of the magnetic amplifying magneto optical system (MAMMOS) with alternative readout fields such as carrier to noise ratio (C/N), eye pattern, jitter and bit error rate (BER), are investigated with a 640 nm wavelength laser diode and 0.55 numerical aperture of the objective lens. The C/N value of 0.12 mu m is 50 dB and is independent of the mark length. A very clear eye pattern was observed. The results show that the jitter value is less than 3% compared with the window width and it is only dependent on the switching speed of the readout field. The error rate is improved by using a thin recording layer of 50 nm in thickness. The minimum domain length which yields a BER of less than 1 x 10(-4) is 0.045 mu m (45 nm); the minimum space length is 0.10 mu m (100 nm). These results are confirmed at a track pitch of about 0.40 mu m. By using a digital versatile disk (DVD) pickup, the areal density can be estimated to be about 23 Gbit/in(2) with the user data capacity of 30 GB/120 mm phi. By using a 400 nm blue laser diode, these values are estimated as 59 Gbit/in(2) and 77 GB/120 mm phi.

DOI： 10.1143/JJAP.39.725

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

The Magnetic Amplifying Magneto-Optical System (MAMMOS) is developed to improve signal-to-noise ratio (SNR). For the MAMMOS, especially the obtained signal is enhanced to the saturated signal level, and also the noise level is kept in the erase level. Hence, S/N for the MAMMOS is sufficient to detect the recorded data.

DOI： 10.1109/INTMAG.2000.872352

Authorship：Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：一般社団法人電子情報通信学会  

MAMMOS(Magnetic AMplifying Magneto-Optical System)is one of the highest density readout methods for storage media. The signal is directly amplified on the medium and its amplitude is just the same as that from a long domain. Even at a 0.04μm domain, the signal was large enough. At a o.2μm packed domain, CNR was more than 50dB and BER was in the 10^<-4> range. By employing a MAMMOS readout with magnetic field modulation(MFM-MAMMOS), the signals have both very high resolution and large amplitude characteristics.

DOI： 10.11485/itetr.23.19.0_33

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

  The results of two-dimensional dynamic calculations performed to simulate the domain transcription process in the readout layer of a magnetostatically coupled dual-layer magneto-optical recording medium and those of one-dimensional calculations made to clarify the nature of the domain wall in the readout layer are given. Detailed time-dependent magnetization behaviors in the readout layer are obtained in the former calculation showing the effect of various parameters such as the atmosphere temperature, stray fields from the recording layer and external fields, on domain transcription. The coercivity of the readout layer is realized by introducing dispersion into the magnitude of the anisotropy constant among computing cells, and the Landau-Lifshitz-Gilbert equation is solved numerically. The magnetization structures in a straight-line wall both in equilibrium and in motion are calculated in the latter calculation.

DOI： 10.3379/jmsjmag.23.S1_151

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

MAMMOS (Magneto Optical Amplifying Magneto Optical System) is one solution to amplify extremely small magneto-optical signal reproduced from a very tiny domain which is recorded as a high areal density. Especially, in the case of MAMMOS with alternative external readout field, the enhanced signal reaches to the saturated signal level, even if the small domain size is 0.1 μm in length which is one tenth compared to the laser spot size. The domain expansion phenomena suddenly happen beyond a critical readout power or external field, that is, it is independent of the domain size. The critical phenomena depend on the critical magneto-static coupling between the expansion layer and the recording layer.

DOI： 10.3379/jmsjmag.23.S1_147

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

MAMMOS (Magnetic AMplifying Magneto-Optical System) is one of the highest density readout methods for storage media. The signal is directly amplified on the medium and its amplitude is just the same as that from a long domain. Even at a 0.04 μm domain, the signal was large enough. At a 0.2 μm packed domain, CNR was more than 50 dB and BER was in the 10-4 range. By employing a MAMMOS readout with magnetic field modulation (MFM-MAMMOS), the signals have both very high resolution and large amplitude characteristics.

DOI： 10.3379/jmsjmag.23.S1_161

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (other academic)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Concerning areal recording density, magnetooptical (MO) disk possesses an advantage compared to another optical disks and also magnetic hard disk (HDD), since the linear density of MO disk can be increased by using a perpendicular magnetic recording, and the track density also can be increased by using an optical tracking method. On the other hand, in the region of high density HDD, demagnetization problem is discussed for archival data storage. However, since the coercive force of MO recording material is over five times larger than that of HDD, it does not become such a sever problem for MO recording. In case of very-high-density recording, the readout signal is drastically reduced due to decreasing both the recorded domain size and the optical resolution. However, in the case of MO, the small readout signal can be enhanced by using a novel readout technique named as magnetic amplifying MO system and the extremely small signal also can be detected. Thus, it is found that the MO has probability of achieving an extremely high density storage such as 100 Gb/in 2.

DOI： 10.1109/2944.735766

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人映像情報メディア学会  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本工業出版  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

For higher density MO recording, a magnetic domain expansion readout method named MAMMOS has been proposed [1]. Herein we report a novel MAMMOS scheme using an in-plane to perpendicular magnetization changing effect. Expansion readout has been achieved by both a magnetic field modulation method and a light intensity modulation method. A clearly amplified readout signal was reproduced from.repetition of 0.2 mu m packed marks.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Magnetic domain expansion readout under the condition of no alternative magnetic field are studied. The reproduced waveform of a 0.2 mu m domain has a very sharp shape and large amplitude of 70% to the saturated signal level. Therefore, it is found that the linearity of the readout signal including domain expansion phenomenon is maintained as well as a conventional readout, therefore relatively clear reproduced signal of the 0.2 mu m packed domain can be detected.. In order to improve it, the sharper readout waveform must be reproduced by using a gating between the expansion and the recording layers, and the readout signal of the 0.2 mu m packed domain is enlarged two times relative to that without a gating layer.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE  

The MAMMOS (magnetic amplifying magneto-optical system) read-out is achieved by applying an alternating external magnetic field for domain expansion and collapse processes. Since the read-out magnetic domain size is expanded by a magnetic field, a strong enhancement in the amplitude of the read-out signal is expected. The read-out laser power dependence of the MAMMOS signal was measured, and the resolution was estimated empirically. Applying an alternating magnetic field with suitable intensity, MAMMOS read-out was realized for a certain range of read-out laser power. The resolution and the margin of the magnetic field depended on the laser power. Even at a 0.2 μ m domain size, its signal was recognizable without interference at the optimum laser power. A C/N level of over 50 dB was obtained for a 0.2 μ m domain size.

DOI： 10.1109/20.706770

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：日本金属学会  

DOI： 10.2320/materia.37.501

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

Magnetic domain expansion readout is studied without the presence of an alternative magnetic field. The reproduced waveform of a crescent-shaped domain 0.08 μm in length reaches 70% of the saturated signal level. However, a circular domain of 0.3 μm diameter does not expand so much. In the case of crescent domain expansion, it is considered that the copied domain shape is different from the original crescent shape in the recording layer, and that this reduces the magnetic energy. The assumption that the copied domain shape of the expansion layer becomes circular agrees well with the experimental result for the domain expansion ratio.

DOI： 10.3379/jmsjmag.22.337

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

We have studied the feasibility of the 120-mm-sized magneto optical disk system which achieves 6-GB user capacity using an optical pickup with a 640-nm wavelength laser and a 0.6-numerical aperture of the objective lens. We have used three technologies: a laser-pulsed magnetic-field modulation recording, a center-aperture-detection type of magnetically-induced super resolution disk with a 0.6-mm-thick single substrate and partial response equalization with maximum likelihood detection. We have evaluated the system-margins of write power, radial tilt, tracking and focusing offset and have confirmed the feasibility of the linear bit density of 0.235 mu m/bit in 0.6-mu m track pitches.

DOI： 10.1143/JJAP.37.2150

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have investigated an in-plane magnetized readout-layer-based magnetic domain expansion phenomenon in a magneto-optical (MO) medium. Very high-density 0.2 mu m packed domains are expanded up to three times the readout signal level in comparison with the conventional approach of applying alternative external field in the readout process. This result suggests that more than 10 Gbits/in.(2) MO recording density may be achieved by implementing the domain expansion technique, using even the currently available 680 nm laser and numerical aperture of 0.55. (C) 1998 American Institute of Physics.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The magneto-optically recorded marks with magnetic field modulation method were studied using spin-polarized scanning electron microscopy. We confirmed that marks with as short a length as 0.1 mu m could be written repeatedly even with laser spot sizes about 1.2 mu m. This mark length is less than 1/6 that of present commercial products. (C) 1998 American Institute of Physics.

DOI： 10.1063/1.120666

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：一般社団法人 映像情報メディア学会  

An amplifyed magneto-optical signal readout using a dynamic domain expansion effect was proposed and experimentally confirmed. The packed domain of 0.2-0.4μm were expanded to saturated signal level by using an alternative external readout field of 0.2-0.4μm period. And also a crescent-shaped domains 0.08μm in length were expanded on the expansion readout layer copied from the recording layer under the condition of no alternative external field. These result reviels that the areal recording density of over 10 Gbit/in^2 with a 680-nm- wavelength laser should be realised.

DOI： 10.11485/itetr.22.15.0_25

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：公益社団法人 日本磁気学会  

A smoothed underlayer surface produces a low level of disk noise in unrecorded disks and a high level of recording noise generated by recording marks. To achieve high S/N disks, the recording noise must be suppressed. By investigating the domain wall motion, we examined the origin of the high recording noise and studied ways of reducing it. When a flat underlayer was used, we found that the high recording noise was caused by irregular domain shapes that resulted from the decrease in the number of domain-wall-pinning sites. A possible cause of the irregular domain shapes is the smaller coercivity of Fe-rich disks and the larger contracting force acting on the domain wall in Tb-rich disks. When we deposited an improved TbFeCo film at a higher Ar pressure in order to create more wall-pinning sites, the recording noise was suppressed at about 4 dB in TM-rich disks, while the disk noise remained low.

DOI： 10.3379/jmsjmag.22.1339

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

  A magnetic amplifying magneto-optical system (MAMMOS) which can expand a size of a small domain is one of the most promising candidates for ultra high density MO storage. Since the MAMMOS read-out consists of both domain expansion and collapse processes, it is important to understand the behavior of the aperture of the read-out layer in order to optimize laser power to achieve higher resolution. This paper reports on the aperture state and the read-out response, when an alternating magnetic field is applied. It is shown that domain expansion and collapse processes occur many times for every 0.4 <i>μ</i> m sized domain and that the shape of the read-out signal is very square. Additionally the number of times that the domain expands and collapses decreases by lowering laser power, which means that the aperture area becomes restricted. It was also confirmed that both expansion and collapse times are much faster than the transient time of the circuit with a band width of 20 MHz, and it is independent of the read-out velocity.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

  The crescent shaped 0.1 <i>μ</i>m domain recorded on the MAMMOS disk is expanded without an alternative external magnetic field and the amplitude of the MO signal is enhanced 5 times larger than that of a conventional disk. Moreover, in the region of the linear velocity (2.5 ∼15 m/sec), the readout waveform does not change and also the signal amplitude of the 0.1<i>μ</i>m domain is kept around 70% compared to the saturated signal level. This result shows the domain expanding speed (also shrinking speed) is much faster than 15 m/sec. Since the rapid domain expansion happens at only central part of laser spot, 0.2<i>μ</i>m packed domains which is beyond readout resolution can be reproduced under the testing condition of 680nm laser diode and 0.55 objective lens.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The read-out signal patterns by MAMMOS were classified and suitable read-out parameter (laser power, magnetic field) was estimated. By adjusting these parameters, both 0.2 mu m size packed domain and modulated domains (T=0.2 mu m) could be reproduced. The MAMMOS read-out from variously lengthed domains and eye pattern were obtained by application of a magnetic field synchronized with clock marks embossed on the disk.

Authorship：Last author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本応用磁気学会  

An amplified magneto-optical signal readout using a dynamic domain expansion effect was proposed and experimentally confirmed. Crescent-shaped domains 0.08μm in length were expanded on the expansion readout layer copied from the recording layer. An amplified readout signal up to five times larger than that of a conventional disk was achieved. From the results of the expansion readout, namely, a 0.08-μm domain length and a 0.4-μm domain width, the areal recording density can be estimated at about 20 Gbit/in^2 with a 680-nm-wavelength laser and at about 60 Gbit/in^2 with a 406-nm-wavelength laser.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

An advanced readout technique on using a dynamic domain expansion phenomenon has been proposed and investigated. Very small domains of 0.08 mu m which achieve an areal density of 20Gb/in(2) (CD single side 30GB with 680nm laser) expand during readout, causing the readout signal to increase to the same level as for 0.6 mu m domain.

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

A readout method to amplify the MO signal by using a magnetic domain expansion phenomenon have been proposed. It was found that the small MO signal reproduced from 0.08 μm crescent shaped domain was amplified 5 times larger than that of conventional disk without readout field. Also the reproduced signal level reaches to about 70% of the saturated signal amplitude. The result corresponds to 20 Gbit/in2 areal density with conventional 680 nm laser.

DOI： 10.1117/12.280702

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

An amplified magneto-optical signal readout by using a dynamic domain expansion effect has been proposed and experimentally confirmed. Small domains of around 0.3 μm in diameter were expanded by a pulsed external field on the readout layer copied from the recording layer. An amplified readout signal up to three times larger than that of the original one has been achieved. © 1996 American Institute of Physics.

DOI： 10.1063/1.116963

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

Fine domain structures of a ferromagnetic specimen can be visualized by deposition of ultrafine ferromagnetic particles onto its surface. We have applied various ferromagnetic particles, such as Co, Fe, Co-Fe alloy and Permalloy, to observation of high-density recording states of thin-film recording media. These studies have revealed that single-domain particles mainly contribute to the domain pattern contrast, while very small superparamagnetic particles are so insensitive to the leakage field from the recording media that they deteriorate the image quality of the domain patterns, Therefore, suppressing the formation of the superparamagnetic particles is effective in improving the resolution and the image quality of the observed domain patterns. In order to suppress the formation of superparamagnetic particles, we have attempted to synthesize hcp-Co particles with large uniaxial anisotropy by alloying Co with some elements which increase the fcc double left right arrow hcp transformation temperature, but all the Co and Co-alloy particles exhibit a pure high-temperature fcc phase.

DOI： 10.1143/JJAP.35.1724

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

  We observed the shape and size of marks recorded magneto-optically on TbFeCo film, using spin-polarized scanning electron microscopy (spin SEM). We studied the laser power dependency of the marks recorded on a land/groove substrate. When larger power was used, the land/groove border acted as a barrier to the propagation of the magnetization reversal, which confirms the advantage of using a land/groove substrate for high-density recording. We also looked at the film roughness dependency of the marks. We found that the magnetization reversal processes depend on the underlayer roughness, which is related to the irregularity of the mark shapes and the recording noise.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Inst of Physics  

Complex magnetization of the damaged track which was possibly created by a local compensation temperature shift at the track center, and reduction of the coercive force at the damaged region are observed. Changes in magnetic characteristics of the amorphous TbFeCo membrane are possibly induced by crystallographic mutation of the film. The decrement in the coercive force at the track center supports the possibility of structural relaxation.

DOI： 10.1063/1.114501

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人映像情報メディア学会  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

A structural analysis of amorphous TbFeCo films has been performed by using EXAFS of as-deposited and annealed samples. It is found that the numbers of inplane Fe-Fe (and Fe-Co) pairs for as-deposited TbFeCo are larger than in the perpendicular direction. On the other hand, in the case of the annealed samples, the number of in-plane Fe-Fe pairs is smaller than in the perpendicular direction. Thus, the direction of the structural anisotropy of the TbFeCo film changes 90 degree due to the annealing procedure. However, the direction of the perpendicular magnetic anisotropy of the TbFeCo does not change before and after the annealing procedure.

DOI： 10.3379/jmsjmag.19.S1_221

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

TbFeCo magneto-optical single layer disks with different compositions have been investigated for recording of small size domains. Using a 830 nm wavelength laser, circular shaped domains with a diameter of 0.25 μm diameter could successfully be written. A low writing stability, dependent on the applied field, was found when recording domains smaller than 0.5 μm on a transition metal rich disk. On the contrary, a high writing stability was achieved on a disk with a highly rare earth rich composition. On this disk two 0.25 μm domains could succesfully be written as close as 0.1 μm to each other. It was also possible to use this single layer TbFeCo disk for recording of domains with widths of 0.1 μm.

DOI： 10.3379/jmsjmag.19.S1_113

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

Pt/Co films with thicker Co bottom and top layers improve the magnetic sensitivity of Pt/Co multilayer disks. By increasing the Co bottom and top layer thickness into 7Å in Pt8Å/Co3Å disks, the magnetic sensitivity is improved to an erasing field of -150 Oe and a writing field of 150 Oe, whereas in a conventional disk an erasing field of more than -400 Oe and a writing field of 300 Oe are needed. Carrier level increases because the total Co thickness is larger. Therefore, compared with a conventional Pt/Co disk, 1 dB higher carrier to noise ratio is obtained. Improved Pt/Co disks using thicker Co layers are promising candidates for high density magneto-optical disks using a short wavelength laser and a magnetic field modulation method.

DOI： 10.3379/jmsjmag.19.S1_149

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

  Co/Pt multilayer films developed for magneto-optical recording are studied as perpendicular magnetic recording media. Recording characteristics of Co/Pt multilayer film deposited on a 3.5" magnetic disk substrate, are evaluated using a thin film ring head for recording and compared with those of a single layer Co-Cr-Ta perpendicular recording medium. The results of recording current characteristics and recording density rolloff performance show that the medium is suitable for perpendicular magnetic recording. The medium noise is, however, about two times as large as that of Co-Cr-Ta medium when a high density signal is recorded. Magnetization structure observation indicates that the medium noise is originating from the irregularities of magnetization transitions.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Domain size changes due to thermal relaxation after high laser power irradiation on amorphous TbFeCo films were studied. In order to achieve mark edge recording for high-density magneto-optical memory, accurate domain size recording is required even after a million erase/write cycles. Highly accelerated erase/write test was performed on typical recording media, rare-earth (RE) -rich and transition-metal (TM) -rich disks. The elongation of the domain size written on the TM-rich film after erase/write cycles was clearly evident
however, the change in the domain size of RE-rich films was small. The small domain size change of the RE-rich disk can be explained in terms of the rapid increase in the coercive force with decreasing temperature and the smaller domain-wall driving force at recording temperature than those for the TM-rich disk, even though both have the same level of structural relaxation.

DOI： 10.1063/1.356806

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

The write/erase cyclability of Co-rich Pt/Co disks was studied, along with factors limiting the cyclability. Annealing experiments suggested that a decrease in CNR results from degradation of the perpendicular magnetic anisotropy in a Pt/Co film heated by an erasing laser beam. The main mechanism of degradation is atomic intermixing at the interface in Pt/Co multilayers. In the case of a Pt/Co film exposed to air, Co might be oxidized during erase cycles. The higher peak temperature of Pt/Co films accelerates the intermixing. Therefore, the number of cycles was increased by adding a heat-diffusive layer to the Pt/Co film in order to lower the peak temperature. For example, Au-coated Pt/Co disks were capable of 105 cycles as a result of a lower peak temperature (430°C), whereas SiN-coated Pt/Co disks, with a peak temperature of 770°C, were capable of only 102 cycles. © 1994 IEEE

DOI： 10.1109/TJMJ.1994.4565897

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

Write/erase cyclability for mark-edge recording is studied using rare-earth element[RE]-rich TbFeCo media. Mark-edge jitter for the (1-7) random pattern is small enough even after millions of cycles of data writing and erasing.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The magneto-optical Kerr effect and magnetic properties of RE-TM/Pt multilayers are investigated (RE-TM = TbCo, TbFeCo, GdTbFeCo). The Kerr rotation of the RE-TM/Pt multilayers with amorphous Pt layers is larger than that of the Pt/Co multilayer in the region of 550-800 nm wavelength for next generation high-density magneto-optical memory. © 1993.

DOI： 10.1016/0304-8853(93)90685-U

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

The extra-ordinary Hall effect has been studied in Ar sputtered Pt(x angstrom)/Co(5 angstrom) and Xe sputtered Pt(x angstrom)/Co(3 angstrom) multilayers with coercivity less-than-or-equal-to 8 kA/m and greater-than-or-equal-to 72kA/m at RT, respectively. The Hall resistivity-rho(H) was found to be larger and have a different Pt layer thickness dependence for the Ar sputtering case as x was varied from 5 angstrom to 20 angstrom, although the ohmic resistivity-rho(R) and the saturation magnetization exhibit similar behavior. The estimated values for rho(H), rho(R), Hall conductivity-gamma(HS) and extra-ordinary Hall coefficient R1 for a hypothetical "multilayer" Co film (x = 0) are all larger than those for "pure" sputtered Co films. Moreover, it was not possible to explain the observed variation of rho(H) with the Pt layer thickness with the short-circuiting effect from the non-magnetic Pt layers as predicted by a simple two-layer model. We suggest that the smaller-rho(H) for the Xe sputtered Pt/Co films compared to Ar sputtered films can be attributed to reduced scattering suggesting a beneficial influence of the interface sharpness on the anisotropy of Pt/Co multilayers.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

It is shown in Fe/Cu bilayered films that the magneto-optical polar Kerr rotation can be enhanced by an effect of the plasma resonance of the free charge carriers in Cu. The strong enhancement is observed around 560 nm which corresponds to the plasma edge of Cu metal. The magnitude of the Kerr rotation reaches up to above twice as large as that of Fe. This is the first example of substantial enhancement of Kerr rotation without use of the interference effect. © 1988 The American Physical Society.

DOI： 10.1103/PhysRevLett.60.1426

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 日本磁気学会  

Layered structure and magnetic and magneto-optical properties of Co/Au and Fe/Au compositionally modulated multilayered films (CMF's) prepared by RF sputtering method were investigated. Modulation length (<i>D</i>) varied from about 10 Å to more than 100 Å. Many satellite peaks were observed in high angle diffraction patterns of the both multilayered films. It was found that the values of magneto-optical Kerr rotation (<i>θ</i><sub>K</sub>) are low and the spectra is simple if the case of relatively small <i>D</i>, however, a new peak of <i>θ</i><sub>K</sub> appears at around λ = 500 nm, corresponding to the absorption edge of Au metal, with the increase of <i>D</i>. Moreover, it was also found that perpendicular anisotropy (<i>K</i><sub>u</sub>) is induced gradually with decreasing <i>D</i> in both CMF's. Perticularly, <i>K</i><sub>u</sub> of Co/Au CMF's becomes positive in the range of relatively large <i>D</i>.

DOI： 10.3379/jmsjmag.11.325

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

The wavelength dependence of polar magneto-optical Kerr rotation (θK) and the structure of Fe/Cu compositionally modulated multilayered films with the modulation length (D) up to ∼95 Å were investigated. It has been found that values of θK are low and Kerr rotation spectra are simple in wavelength region between 250 and 800 nm for the films with relatively small D. However, a new peak of θK appears at around 560 nm, corresponding to the absorption edge of Cu metal, and becomes large with the increase of D. The new peak moves towards the longer wavelength side with the increase of thickness ratio (Fe/Cu) of Fe to Cu layers.

DOI： 10.1063/1.338463

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

The structure, magnetic properties, polar Kerr rotation angle (θk), and Mössbauer effect of Fe/Cu and Co/Cu system compositionally modulated multilayered films were studied. No satellite peak was found in the Fe/Cu film X-ray diffraction pattern, but a clear satellite peak was observed in that of the Co/Cu system multilayered film, revealing the difference between the structures of the Fe/Cu and Co/Cu multilayered films. A new θk peak was observed at λ = 560 nm in the multilayered films with thick composition modulation period. The appearance of the new θk peak at this wavelength suggests the possibility of a new electron transition, because no multiple reflection was observed in the neighborhood of 560 nm. © 1987 IEEE.

DOI： 10.1109/TJMJ.1987.4549371

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

The changes in structure and saturation magnetization (4πMs) due to composition modulation period (D), Curie temperature (Tc), perpendicular magnetic anisotropy (Ku), and polar Kerr rotation in composition modulated multilayered films with amorphous Zr-Fe films and amorphous Tb-Fe films superimposed were studied. It was found that as D1, the composition modulation period calculated from the first X-ray diffraction peak, gets thinner, 4πMs increases. This can be explained by the fact that magnetization of Fe within the Zr-Fe film is induced by the Tb-Fe film. © 1987 IEEE.

DOI： 10.1109/TJMJ.1987.4549372

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOCIETY JAPAN  

The wavelength dependence of polar magneto-optical Kerr rotation angle ($\theta_{\text{K } }$) was measured in compositionally modulated multilayered films (CMF) composed of Co/Cu, Fe/Cu, Co/Au and Fe/Au systems. The value of $\theta_{\text{K } }$ is low and the shape of wavelength dependence is relatively flat in the CMF with modulation length less than nearly 20Å. However, a new $\theta_{\text{K } }$ peak appears at around $\lambda{=}560$ nm in Co/Cu and Fe/Cu CMF and around $\lambda{=}500$ nm in Co/Au and Fe/Au CMF with large modulation length. These wavelengths correspond to the absorption edge of Cu and Au metals, respectively.

DOI： 10.1143/JPSJ.55.2539

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/TJMJ.1985.4548580

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Ge-Sb-Te alloy thin films have widely been available as a recording material for optical recording media such as DVD and Blu-ray on the point of view of its large contrast on refractive index (or reflection) in between the crystalline and amorphous states. Using its large contrast on electric resistance (〜3 orders of magnitude), on the other hand, the next generation non-volatile memory has been developed as well, and 1-GB class phase change memory (PCM) has been successfully shipped to the market. On the way of PCM research, a new type of PCM has been invented, replacing the Ge-Sb-Te alloy film into a GeTe/Sb_2Te_3 superlattice, which enables to suppress the switching energy by 1/10, holding more than one billion write-erase cycles. Very recently, in the superlattice we noticed and found several unusual properties, which have never been observed in the alloy films with the same composition. It is recently suggested by solid-state and theoretical physicists that the unusual phenomena are related to topological insulator, which is a new physics predicted in 2005. In this paper, we report and discuss the unusual mirror-symmetric magneto-optical Kerr-rotation observed from the superlattice.

Language：Japanese   Publisher：映像情報メディア学会  

Language：English  

Language：Japanese   Publisher：The Physical Society of Japan  

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_318_3

Language：Japanese   Publisher：三重銀行  

Language：Japanese   Publisher：The Physical Society of Japan  

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日経ＢＰ社  

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本磁気学会  

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：ニューメディア  

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本応用物理学会  

Language：English   Publisher：JAPAN J APPLIED PHYSICS  

Read/write characteristics of the magnetic amplifying magneto optical system (MAMMOS) with alternative readout fields such as carrier to noise ratio (C/N), eye pattern, jitter and bit error rate (BER), are investigated with a 640 nm wavelength laser diode and 0.55 numerical aperture of the objective lens. The C/N value of 0.12 mu m is 50 dB and is independent of the mark length. A very clear eye pattern was observed. The results show that the jitter value is less than 3% compared with the window width and it is only dependent on the switching speed of the readout field. The error rate is improved by using a thin recording layer of 50 nm in thickness. The minimum domain length which yields a BER of less than 1 x 10(-4) is 0.045 mu m (45 nm); the minimum space length is 0.10 mu m (100 nm). These results are confirmed at a track pitch of about 0.40 mu m. By using a digital versatile disk (DVD) pickup, the areal density can be estimated to be about 23 Gbit/in(2) with the user data capacity of 30 GB/120 mm phi. By using a 400 nm blue laser diode, these values are estimated as 59 Gbit/in(2) and 77 GB/120 mm phi.

DOI： 10.1143/JJAP.39.725

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本光学会  

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：IEEE  

Language：English   Publisher：Elsevier  

The domain observation technique using fine magnetic particles as small as 10 nm is very effective in investigating the high density recording states of various kinds of magnetic and magneto-optic recording media. Theoretical calculations predict that suppression of thermal agitation of spins within each particle greatly improves the image quality of observed domain patterns. This prediction has been experimentally verified by varying the sample temperature during evolution of the domain patterns. As the sample temperature decreases, high density recording states can be visualized more clearly and definitely owing to the suppression of thermal agitation of the spins.

DOI： 10.1016/S0304-8853(97)00187-X

Language：Japanese  

Language：Japanese   Publisher：The Magnetics Society of Japan  

Ultra high-density-recording states were observed in magneto-optical (MO) and magnetic recording media, using particles prepared by sputtering. We clearly observed recording bits as small as 0.3μm in diameter for MO media,and also visualized the influence of the recording laser power on high-density recording states. The observation method also made it possible to observe ultra-high-density recording states (with a bit length of 0.08μm) in obliquely evaporated Co-CoO magnetic recording media. According to these experimental results, the resolution of the present method was estimated to be finer than 0.08μm.

DOI： 10.3379/jmsjmag.19.89

Language：Japanese   Publisher：The Institute of Image Information and Television Engineers  

TbFeCo magneto-optical single layer disk with different compositions have been investigated for recording of small size domains with 830nm wavelength laser. A low writting stability, dependent on the applied field, was found when recording domains smaller than 0.5 μm on a transition metal rich disk. On the contrary, a high writing stability was achieved on a disk with a highly rare earth rich composition. These phenomena can be explained by using the Huth model for domain formation.

Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

To make higher density on optical disk,a new recording method- two dimensional recording- which can increase the track-density rather than the linear density was proposed.The perfomiance of this method on increasing density is estimated by the simulation and confirmed by measuring the read-out signal.Consequently,it is clarified that this method can attain more than twice the areal density independently and realize the density of 2.2 Gbit, in^2 which is 8 times as large as that of first generation using 680 nm laser diode.

Language：English   Publisher：The Institute of Image Information and Television Engineers  

To make higher density on optical disk, a new recording method-two dimensional recording- which can increase the track-density rather than the linear density was proposed. The performance of this method on increasing density is estimated by the simulation and confirmed by measuring the read-out signal. Consequently, it is clarified that this method can attain more than twice the areal density independently and realize the density of 2.2 Gbit/in^2 which is 8 times as large as that of first generation using 680 nm laser diode.

Language：Japanese   Publisher：The Magnetics Society of Japan  

  Write/erase cyclability on Co-rich Pt/Co disks was studied, along with its limiting factors. Annealing experiments suggested that a decrease in CNR resulted from degradation of the perpendicular magnetic anisotropy in a Pt/Co film heated by an erasing laser beam. The main mechanism of the degradation is atomic intermixing at the interface in Pt/Co multi-layers. In the case of a Pt/Co film exposed to air, Co might be oxidized during the erasing cycles. The higher peak temperature of Pt/Co films accelerates the intermixing. Therefore, the number of cycles was increased by adding a heat-diffusive layer to the Pt/Co film in order to decrease the peak temperature. For example, Au-coated Pt/Co disks were capable of 10<sup>5</sup> cycles, on account to the lower peak temperature (430°C), whereas SiN-coated Pt/Co disks, whose peak temperature was 770°C, were capable of only 10<sup>2</sup> cycles.

DOI： 10.3379/jmsjmag.17.809

Language：Japanese   Publisher：一般社団法人映像情報メディア学会  

Language：Japanese   Publisher：The Institute of Image Information and Television Engineers  

DOI： 10.11485/tvtr.16.16_43

Language：Japanese   Publisher：The Physical Society of Japan  

Language：Japanese   Publisher：The Physical Society of Japan  

Language：Japanese   Publisher：The Physical Society of Japan  

Language：Japanese   Publisher：一般社団法人 日本物理学会  

Language：Japanese   Publisher：The Magnetics Society of Japan  

Magnetic and magneto-optical properties of amorphous Zr-Fe/Tb-Fe composition modulated multilayered films (CMF) prepared by RF sputtering technique were investigated. In this system, a composition modulation period (<i>D</i>) more than 40 Å was confirmed by the low angle X-ray diffraction method. Curie temperature (<i>T</i><sub>c</sub>) of these multilayered films falls with decreasing <i>D</i>, but saturation magnetization (<i>M</i><sub>s</sub>) and perpendicular anisotropy (<i>K</i><sub>u⊥</sub>) increase with decreasing <i>D</i>. Sharpening of hyperfine field distribution was observed with the decrease of <i>D</i>. Wavelength dependences of magneto-optical Kerr rotation (<i>θ</i><sub>K</sub>) are independent of the variation of <i>D</i>.

DOI： 10.3379/jmsjmag.10.291

Language：Japanese   Publisher：一般社団法人 日本物理学会  

Language：Japanese   Publisher：一般社団法人 日本物理学会  

Language：Japanese   Publisher：一般社団法人 日本物理学会  

Language：Japanese   Publisher：一般社団法人 日本物理学会  

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