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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：0 パーセンタイル：0(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.
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：59.75(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：17.84(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：7.86(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：45.99(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.
