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廣畑 貴文*; Lloyd, D. C.*; 窪田 崇秀*; 関 剛斎*; 高梨 弘毅; 介川 裕章*; Wen, Z.*; 三谷 誠司*; 小泉 洸生*
IEEE Access, 11, p.117443 - 117459, 2023/10
被引用回数：1 パーセンタイル：0.00(Computer Science, Information Systems)Spintronic devices are expected to replace the recent nanoelectronic memories and sensors due to their efficiency in energy consumption and functionality with scalability. To date, spintronic devices, namely magnetoresistive junctions, employ ferromagnetic materials by storing information bits as their magnetization directions. However, in order to achieve further miniaturization with maintaining and/or improving their efficiency and functionality, new materials development is required: 1) increase in spin polarization of a ferromagnet or 2) replacement of a ferromagnet by an antiferromagnet. Antiferromagnetic materials have been used to induce an exchange bias to the neighboring ferromagnet but they have recently been found to demonstrate a 100% spin-polarized electrical current, up to THz oscillation and topological effects. In this review, the recent development of three types of antiferromagnets is summarized with offering their future perspectives towards device applications.
山崎 匠*; 関 剛斎*; 窪田 崇秀*; 高梨 弘毅
Applied Physics Express, 16(8), p.083003_1 - 083003_4, 2023/08
被引用回数：0 パーセンタイル：0.00(Physics, Applied)We report the effect of the epitaxial growth of NiO films on its spin current transmission. Two sample series of Pt/NiO/CoFeB, including epitaxial and polycrystalline NiO, were prepared using different deposition conditions. The spin current transmission of NiO is evaluated using the thermo-spin effects in the trilayers. Epitaxial NiO exhibits a non-monotonic behavior in the NiO thickness dependence of spin current transmission, while this behavior is smeared out in polycrystalline NiO. The non-monotonic behavior implies the presence of multiple spin transport mechanisms, which becomes apparent with epitaxial growth.
Zhou, Z.*; Frost, W.*; Lloyd, D. C.*; 関 剛斎*; 窪田 崇秀*; Ramos, R.*; 齊藤 英治; 高梨 弘毅; 廣畑 貴文*
Journal of Magnetism and Magnetic Materials, 571, p.170575_1 - 170575_5, 2023/04
被引用回数：1 パーセンタイル：0.00(Materials Science, Multidisciplinary)Recent development in neuromorphic computation allows us to achieve low power and highly efficient calculations better than the conventional von Neumann computation. In order to achieve realistic synaptic operation, potentiation to add weighting to strengthen a selected artificial synapse. Such functionality can be achieved by reducing the electrical resistance of the artificial synapse. Recently, a ferromagnetic Heusler alloy used in a magnetoresistive junction has been demonstrated to crystallise via the layer-by-layer mode by introducing an electrical current pulse. In this study, we have extended the current-induced crystallisation to a junction with epitaxially-grown Heusler alloy after post-annealing for crystallisation. By combining this potentiation functionality with the neuromorphic operation, realistic synaptic computation can be developed.
MnSi重田 出*; Oku, Shuta*; 窪田 崇秀*; 木村 尚次郎*; 関 剛斎*; 篠崎 文重*; 淡路 智*; 高梨 弘毅; 廣井 政彦*
AIP Advances (Internet), 13(2), p.025116_1 - 025116_5, 2023/02
被引用回数：0 パーセンタイル：0.00(Nanoscience & Nanotechnology)Superconducting properties were investigated in epitaxially layered films consisting of superconductor NbN and half-metallic Heusler alloy CoMnSi(CMS). Temperature dependence of the electrical resistivity 
(T) was measured by applying perpendiar magnetic fields to the surface of NbN/CMS films. With the increase of the CMS thickness 
, the upper critical field 
H
decreased monotonically, but the superconducting transition temperature T
had the minimum of 10.1 K at 
5 nm. The T behavior was in qualitative agreement with the theory of the 
-coupling. The pair-breaking parameter 
determined by the superconducting fluctuation theory took the maximum at = 3
5 nm, which would be related to the minimum of 
. The experimental results reveal that the superconductivity of the NbN layer in NbN/CMS films is affected by the interplay between the superconducting NbN layer and the half-metallic CMS layer.
CoGa
films窪田 崇秀*; 高野 大地*; 小田 洋平*; Mohanty, S.*; 伊藤 啓太*; 松木 充弘*; 林田 誠弘*; Sun, M.*; 竹田 幸治; 斎藤 祐児; et al.
Physical Review Materials (Internet), 6(4), p.044405_1 - 044405_12, 2022/04
被引用回数：5 パーセンタイル：43.81(Materials Science, Multidisciplinary)This study focuses on an inverse-type Heusler alloy, MnCoGa (MCG), with a small off-stoichiometry (), showing perpendicular magnetic anisotropy (PMA). We observed a relatively large uniaxial magnetocrystalline anisotropy constant (
) on the order of 10
J/m
at room temperature in the MCG films with a small tetragonal distortion of a few percent. X-ray magnetic circular dichroism (XMCD) was employed to get insight into the origin for the PMA. Negligible angular variation of the orbital magnetic moment evaluated using the XMCD spectra suggested a minor role of the so-called Bruno's term to . The origin of the PMA was discussed based on the second-order perturbation theory in terms of the spin-orbit coupling, and first principles calculations, claiming that the mixing of the occupied 
- and the unoccupied 
-spin states is responsible for the PMA of the MCG films.
VAl/Fe layered films showing exchange bias窪田 崇秀*; 嶋田 雄介*; 土屋 朋生*; 吉川 智己*; 伊藤 啓太*; 竹田 幸治; 斎藤 祐児; 今野 豊彦*; 木村 昭夫*; 高梨 弘毅*
Nanomaterials (Internet), 11(7), p.1723_1 - 1723_11, 2021/07
被引用回数：2 パーセンタイル：13.44(Chemistry, Multidisciplinary)Heusler alloys exhibit various magnetic properties. In this study, a layered sample consisting of a Heusler alloy, MnVAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered MnVAl is known as a ferrimagnet, the MnVAl/Fe layered structure exhibits exchange bias. The high-angle annular dark field STEM images demonstrated the formation of MnVAl clusters with the L2
phase distributed only around the interface to the Fe layer in the sample. Furthermore, the antiferromagnetic coupling between the Mn- and Fe-moments were observed in element specific hysteresis loops measured using XMCD. The locally ordered L2 phase and antiferromagnetic Mn-moments in the MnVAl layer are important for the exchange bias.
Frost, W.*; 関 剛斎*; 窪田 崇秀*; Ramos, R.*; 齊藤 英治; 高梨 弘毅*; 廣畑 貴文*
Applied Physics Letters, 118(17), p.172405_1 - 172405_5, 2021/04
被引用回数：1 パーセンタイル：5.74(Physics, Applied)We demonstrate that the spin-Seebeck effect can be used to estimate the volume of edge domains formed in a giant magnetoresistive (GMR) device. The thermal gradient induced by Joule heating can be harnessed by the addition of a ferromagnetically insulating channel of Fe
O
on the sides of the GMR pillar. This generates a spin wave in FeO, which couples with the free-layer edge magnetization and controls the reversal of the ferromagnetic layers in one direction only, increasing the current density from 
A/cm
to 
A/cm. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be 
by spin-transfer torque.
VAl Heusler alloy thin films; Appearance of antiferromagnetism and exchange bias in a layered structure with Fe土屋 朋生*; 小林 亮太*; 窪田 崇秀*; 斉藤 耕太郎*; 小野 寛太*; 大原 高志; 中尾 朗子*; 高梨 弘毅*
Journal of Physics D; Applied Physics, 51(6), p.065001_1 - 065001_7, 2018/02
被引用回数：10 パーセンタイル：43.16(Physics, Applied)MnVAl Heusler alloy films were epitaxially grown on MgO(100) single-crystal substrates by ultra-high-vacuum magnetron sputtering. A2- and L21-type MnVAl order was controlled by the deposition temperature. A2-type MnVAl films showed no spontaneous magnetization, while L21-type MnVAl films showed ferrimagnetic behaviour with a maximum saturation magnetization of 220 emu/cm
at room temperature (RT). An antiferromagnetic reflection was observed with neutron diffraction at RT for an A2-type MnVAl film deposited at 400
C. A bilayer sample of the antiferromagnetic A2-type MnVAl and Fe showed an exchange bias of 120 Oe at 10 K.
