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論文

Composition dependence of the anomalous Nernst effect in Fe$$_{4-x}$$Mn$$_{x}$$N and Fe$$_{4-y}$$Co$$_{y}$$N films

Yin, W.*; 伊藤 啓太*; 坪和 優佑*; 辻川 雅人*; 白井 正文*; 梅津 理恵*; 高梨 弘毅

Journal of Magnetism and Magnetic Materials, 628, p.173157_1 - 173157_8, 2025/09

 被引用回数:0

Fe$$_{4}$$N exhibits a large anomalous Nernst effect (ANE), which motivates a systematic study of enhancing the anomalous Nernst coefficient (S$$_{rm ANE}$$) by modulating its electronic and magnetic structures. In this study, Mn and Co substitution effects for Fe in Fe$$_{4}$$N on S$$_{ANE}$$ were investigated. Fe$$_{4-x}$$Mn$$_{x}$$N and Fe$$_{4-y}$$Co$$_{y}$$N films in wide ranges of x and y were grown epitaxially on MgO(001) and (LaAlO$$_{3}$$)$$_{0.3}$$(Sr$$_{2}$$TaAlO$$_{6}$$)$$_{0.7}$$(001) substrates, respectively, using molecular beam epitaxy. The S$$_{rm ANE}$$ value of the Fe$$_{4}$$N film is suppressed by substituting Fe with Mn or Co. By measuring the ANE, Seebeck effect, and anomalous Hall effect, the transverse thermoelectric conductivity ($$alpha_{xy}$$) was evaluated. The composition dependence of S$$_{ANE}$$ was dominated by the change of $$alpha_{xy}$$ for both Fe$$_{4-x}$$Mn$$_{x}$$N and Fe$$_{4-y}$$Co$$_{y}$$N films. First-principles calculations were conducted for the transverse electric conductivity ($$sigma_{xy}$$) and $$alpha_{xy}$$ of Fe$$_{4}$$N and Fe$$_{3.1}$$Co$$_{0.9}$$N, and large $$alpha_{xy}$$ leading to large S$$_{ANE}$$ was predicted in Fe$$_{3.1}$$Co$$_{0.9}$$N.

論文

Magnetoelastic coupling for Fe-Ga thin films epitaxially grown on different substrates

Ding, H.*; 伊藤 啓太*; 遠藤 恭*; 高梨 弘毅; 関 剛斎*

Journal of Physics D; Applied Physics, 57(38), p.385002_1 - 385002_10, 2024/09

 被引用回数:2 パーセンタイル:62.71(Physics, Applied)

This paper reports the systematic study on the structure, magnetic properties and magnetoelastic properties for the Fe$$_{100-x}$$Ga$$_{x}$$ (001) thin films epitaxially grown on the different substrates of GaAs(001) and MgO(001) using the sputtering technique. The alloy composition dependence of effective magnetoelastic coupling coefficient B$$_{eff}$$ along the FeGa [110] direction indicated that the largest magnetoelastic coupling was obtained for the Fe-Ga layer with x = 30 grown on the MgO substrate. Considering the results of structural analysis and magnetization measurement, the different crystallite sizes depending on the kind of substrate may give rise to the different magnetoelastic coupling strengths between the Fe-Ga layers on the MgO and the GaAs. The magnetostriction along the FeGa [111] direction was also estimated with the assumption of plausible elastic property of Fe-Ga, and showed the values comparable to the reported value of bulk Fe-Ga. This means the large magnetostriction can be obtained even for the Fe-Ga thin films epitaxially grown not only on the GaAs(001) but also on the MgO(001). The findings in this work will give a guideline for designing spintronic applications with a Fe-Ga layer exhibiting a large magnetoelastic coupling.

論文

薄膜の垂直磁気異方性

高梨 弘毅; 関 剛斎*

まぐね, 19(3), p.100 - 106, 2024/06

薄膜の垂直磁気異方性は、磁気記録のみならずスピントロニクスにおいても重要な役割を果たしている。本解説記事では、垂直磁気異方性に関して、磁気多層膜、規則合金膜、希土類遷移金属アモルファス合金多層膜、不均一膜やグラニュラー膜など、垂直磁化を持つ具体例を示しながら、基礎からこれまでの研究、そして最近の研究動向を概説する。それぞれの具体例について、構造対称性の破れによる界面磁気異方性、ひずみによる磁気弾性異方性、バルクの結晶磁気異方性、原子の方向性規則配列などの垂直磁気異方性の物理的起源を議論する。

論文

Spin caloritronics in metallic superlattices

関 剛斎*; 内田 健一*; 高梨 弘毅

Journal of Physics; Condensed Matter, 36(33), p.333001_1 - 333001_11, 2024/05

 被引用回数:1 パーセンタイル:17.83(Physics, Condensed Matter)

Spin caloritronics, a research field studying on the interconversion between a charge current (J$$_{rm c}$$) and a heat current (J$$_{rm q}$$) mediated by a spin current (J$$_{rm s}$$) and/or magnetization (M), has attracted much attention not only for academic interest but also for practical applications. Newly discovered spin-caloritronic phenomena such as the spin Seebeck effect (SSE) have stimulated the renewed interest in the thermoelectric phenomena of a magnet, which have been known for a long time, e.g. the anomalous Nernst effect (ANE). These spin-caloritronic phenomena involving the SSE and the ANE have provided with a new direction for thermoelectric conversion exploiting J$$_{rm s}$$ and/or M. Importantly, the symmetry of ANE allows the thermoelectric conversion in the transverse configuration between J$$_{rm q}$$ and J$$_{rm c}$$. Although the transverse configuration is totally different from the conventional longitudinal configuration based on the Seebeck effect and has many advantages, we are still facing several issues that need to be solved before developing practical applications. The primal issue is the improvement of conversion efficiency. In the case of ANE-based applications, a material with a large anomalous Nernst coefficient (S$$_{rm ANE}$$) is the key for solving the issue. This review article introduces the increase of S$$_{rm ANE}$$ can be achieved by forming superlattice structures, which has been demonstrated for several kinds of materials combinations. The overall picture of studies on spin caloritronics is first surveyed. Then, we mention the pioneering work on the transverse thermoelectric conversion in superlattice structures, which was performed using Fe-based metallic superlattices, and show the recent studies for the Ni-based metallic superlattices and the ordered alloy-based metallic superlattices.

論文

Uniaxial magnetic anisotropy of L1$$_{0}$$-FeNi films with island structures on LaAlO$$_{3}$$(110) substrates by nitrogen insertion and topotactic extraction

西尾 隆宏*; 伊藤 啓太*; 藏 裕彰*; 高梨 弘毅; 柳原 英人*

Journal of Alloys and Compounds, 976, p.172992_1 - 172992_8, 2024/03

 被引用回数:3 パーセンタイル:36.88(Chemistry, Physical)

Tetrataenite (L1$$_{0}$$-FeNi) has potential for application in next-generation permanent magnets. This compound is a rare-earth-free material comprising Fe and Ni, which are abundant elements. In addition, an extremely high uniaxial magnetocrystalline anisotropy ($$K$$u) is expected for L1$$_{0}$$-FeNi because of the ordered arrangement of the elements. This study reports the magnetic properties of uniaxially oriented L1$$_{0}$$-FeNi films with island structures fabricated by a novel method involving the radio-frequency sputter deposition of FeNi alloy films onto a LaAlO$$_{3}$$(110) substrate, followed by nitrogen insertion and topotactic extraction. FeNiN(110) films are epitaxially grown on the LAO(110) plane by the nitriding and additional annealing process of the FeNi alloy films at high temperatures under ammonia gas to reduce the volume fraction of crystallographic variants. Uniaxially oriented L1$$_{0}$$-FeNi alloy films with island structures are obtained after the topotactic denitriding of the FeNiN films. The uniaxial magnetic anisotropy of the L1$$_{0}$$-FeNi films is determined from the magnetization curves and via magnetic torque measurements of the films. The obtained L1$$_{0}$$-FeNi film exhibiting a relatively high superlattice order parameter of 0.74 yielded a uniaxial magnetocrystalline anisotropy energy of ~0.63 MJ/m$$^{3}$$ at 300 K, as well as coercivities of 319 and 358 kA/m at 300 and 10 K, respectively. This coercivity is the highest value reported for artificial L1$$_{0}$$-FeNi to date.

論文

Quantitative measurement of figure of merit for transverse thermoelectric conversion in Fe/Pt metallic multilayers

山崎 匠*; 平井 孝昌*; 八木 貴志*; 山下 雄一郎*; 内田 健一*; 関 剛斎*; 高梨 弘毅

Physical Review Applied (Internet), 21(2), p.024039_1 - 024039_11, 2024/02

 被引用回数:2 パーセンタイル:62.71(Physics, Applied)

This study presents a measurement method for determining the figure of merit for transverse thermoelectric conversion in thin-film forms. Leveraging the proposed methodology, we comprehensively investigate the transverse thermoelectric coefficient, in-plane electrical conductivity, and out-of-plane thermal conductivity in epitaxial and polycrystalline Fe/Pt metallic multilayers.

論文

Magnetic layer thickness influence on magnetoelastic properties anisotropy in Co$$_{2}$$Fe$$_{0.4}$$Mn$$_{0.6}$$Si heusler alloy thin films

Nabialek, A.*; Chumak, O.*; 関 剛斎*; 高梨 弘毅; Baczewski, L. T.*; Szymczak, H.*

IEEE Transactions on Magnetics, 59(11), p.2501405_1 - 2501405_5, 2023/11

 被引用回数:2 パーセンタイル:30.27(Engineering, Electrical & Electronic)

The anisotropic magnetoelastic (ME) properties of epitaxial Co$$_{2}$$Fe$$_{0.4}$$Mn$$_{0.6}$$Si(CFMS) Heusler alloy thin films with thicknesses ranging from 8 to 100 nm were investigated using the strain-modulated ferromagnetic resonance (SMFMR) technique. The calculation of the first cubic magnetocrystalline (MC) constant ${it K}$ $$_{1}$$ and the two cubic ME constants ${it b}$ $$_{1}$$ and ${it b}$ $$_{2}$$ was carried out assuming the cubic symmetry of the magnetic layer. A significant negative perpendicular MC anisotropy, of the order of 10$$^{5}$$ J/m$$^{3}$$, was also observed. The investigated parameters were found to be dependent on the thickness of the magnetic layer. The thinnest magnetic layers showed the strongest cubic MC anisotropy and the weakest anisotropy of ME properties. These findings highlight the importance of considering the magnetic layer thickness when evaluating the anisotropy in the ME properties of Heusler alloy thin films.

論文

Antiferromagnetic films and their applications

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:3 パーセンタイル:22.16(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.

論文

Influence of the strain effect on magnetocrystalline anisotropy in Co$$_{2}$$Fe$$_{0.4}$$Mn$$_{0.6}$$Si Heusler alloys

Nabialek, A.*; Chumak, O. M.*; Aleshkevych, P.*; Domagala, J. Z.*; Pacewicz, A.*; Salski, B.*; Krupka, J.*; 関 剛斎*; 高梨 弘毅; Baczewski, L. T.*; et al.

Scientific Reports (Internet), 13, p.17016_1 - 170169, 2023/10

 被引用回数:4 パーセンタイル:50.15(Multidisciplinary Sciences)

The perpendicular magnetocrystalline anisotropy, magnetoelastic properties as well as the Gilbert damping factor in Co$$_{2}$$Fe$$_{0.4}$$Mn$$_{0.6}$$Si thin films were found to depend on a magnetic layer thickness, and they can be also tuned by the application of additional Ag buffer layer. The tetragonal distortion of a magnetic layer was found to increase with decreasing thickness, and after the application of an additional Ag buffer layer, the character of this distortion was changed from tensile to compressive in the plane of a film. A correlation between the tetragonal distortion and perpendicular magnetocrystalline anisotropy was found. However, the magnitude of the observed tetragonal distortion for most samples seems to be too small to explain alone the experimentally found large magnitude of the perpendicular magnetocrystalline anisotropy. For these samples, other mechanisms including both surface and volume effects must be taken into account.

論文

Influence of epitaxial growth on spin current transmission of NiO films

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:1 パーセンタイル:13.37(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.

論文

Intercorrelated anomalous Hall and spin Hall effect in kagome-lattice Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$-based shandite films

Lau, Y.-C.*; 池田 絢哉*; 藤原 宏平*; 小沢 耀弘*; Zheng, J.*; 関 剛斎*; 野村 健太郎*; Du, L.*; Wu, Q.*; 塚崎 敦*; et al.

Physical Review B, 108(6), p.064429_1 - 064429_11, 2023/08

 被引用回数:8 パーセンタイル:74.51(Materials Science, Multidisciplinary)

Magnetic Weyl semimetals (mWSMs) are characterized by linearly dispersive bands with chiral Weyl node pairs associated with broken time-reversal symmetry. One of the hallmarks of mWSMs is the emergence of large intrinsic anomalous Hall effect. On heating the mWSM above its Curie temperature, the magnetism vanishes while exchange-split Weyl point pairs collapse into doubly degenerate gapped Dirac states. Here, we reveal the attractive potential of these Dirac nodes in paramagnetic state for efficient spin current generation at room temperature via the spin Hall effect. Ni and In are introduced to separately substitute Co and Sn in a prototypal mWSM Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ shandite film and tune the Fermi level. Composition dependence of spin Hall conductivity for paramagnetic shandite at room temperature resembles that of anomalous Hall conductivity for ferromagnetic shandite at low temperature; exhibiting peak-like dependence centering around the Ni-substituted Co$$_{3}$$Ni$$_{1}$$Sn$$_{2}$$S$$_{2}$$ and undoped Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ compositions, respectively. The observed spin Hall and anomalous Hall conductivity maxima at different compositions reflect optimum Fermi-level positioning relative to the paramagnetic Dirac and magnetic Weyl states, suggesting the common origin and intercorrelation between the two Hall effects. Our findings highlight a strategy for the quest of spin Hall materials, guided by the abundant experimental anomalous Hall-effect data of ferromagnets in the literature.

論文

金属人工格子を基軸とした先進磁性材料開発と新展開

高梨 弘毅

まてりあ, 62(5), p.301 - 306, 2023/05

金属人工格子とは、異種金属をナノメートルスケールで積層した人工物質である。金属人工格子の研究は、巨大磁気抵抗効果や層間交換結合の観点で、1980年代後半から1990年代前半にかけて、多くの研究がなされた。さらに、金属人工格子の研究はスピントロニクスという新たな分野を生み、21世紀に入りスピントロニクスは大きく成長した。そしてスピントロニクスの発展の中で、今また金属人工格子の新たな有用性が注目されている。本稿では、筆者のこれまでの成果を示しつつ、金属人工格子の研究の流れと最近のトピックスをまとめる。なお、本稿は2023年3月の日本金属学会春期大会での本多記念講演に基づき、原稿化されたものである。

論文

Magnetization switching process by dual spin-orbit torque in interlayer exchange-coupled systems

増田 啓人*; 山根 結太*; 関 剛斎*; Raab, K.*; 土肥 昂尭*; Modak, R.*; 内田 健一*; 家田 淳一; Kl$"a$ui, M.*; 高梨 弘毅

Applied Physics Letters, 122(16), p.162402_1 - 162402_7, 2023/04

 被引用回数:3 パーセンタイル:39.87(Physics, Applied)

We report current-induced magnetization switching in Pt/Co/Ir/Co/Pt multilayers with different Ir layer thicknesses ($$t_mathrm{Ir}$$), where the perpendicularly magnetized Co layers are coupled ferromagnetically or antiferromagnetically through an interlayer exchange coupling and are sandwiched by the Pt spin Hall layers. The domain structures formed during switching vary depending on the magnetization alignment, i.e., ferromagnetically coupled or antiferromagnetically coupled configuration. These results clarify the macroscopic picture of switching process for interlayer exchange-coupled systems. The local picture of the switching process is also examined by a numerical calculation based on a macrospin model, which reveals the switching dynamics triggered by dual spin-orbit torque for both antiferromagnetically and ferromagnetically coupled cases. The numerical calculation shows that the dual spin-orbit torque from the two Pt layers effectively acts on the two Co layers not only for the antiferromagnetically coupled case but also for the ferromagnetically coupled one. Our findings deepen the under- standing of the switching mechanism in a magnetic multilayer and provide an avenue to design spintronic devices with more efficient spin-orbit torque switching.

論文

Current-induced crystallisation in a Heusler-alloy-based giant magnetoresistive junction for neuromorphic potentiation

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:11.20(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.

論文

Superconducting fluctuation effect on epitaxially layered films of superconductor NbN and half-metallic Heusler alloy Co$$_{2}$$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:1 パーセンタイル:13.37(Nanoscience & Nanotechnology)

Superconducting properties were investigated in epitaxially layered films consisting of superconductor NbN and half-metallic Heusler alloy Co$$_{2}$$MnSi(CMS). Temperature dependence of the electrical resistivity $$rho$$(T) was measured by applying perpendiar magnetic fields to the surface of NbN/CMS films. With the increase of the CMS thickness $$d_{rm CMS}$$, the upper critical field $$mu$$$$_{0}$$H$$_{c2}$$ decreased monotonically, but the superconducting transition temperature T$$_{c}$$ had the minimum of 10.1 K at $$d_{rm CMS}$$ $$approx$$ 5 nm. The T$$_{c}$$ behavior was in qualitative agreement with the theory of the $$Pi$$-coupling. The pair-breaking parameter $$delta$$ determined by the superconducting fluctuation theory took the maximum at $$d_{rm CMS}$$ = 3$$sim$$5 nm, which would be related to the minimum of $$T_{rm c}$$. 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.

論文

Electrical detection of domain evolution in magnetic Weyl semimetal Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ submicrometer-wide wire devices

塩貝 淳一*; 池田 絢哉*; 藤原 宏平*; 関 剛斎*; 高梨 弘毅; 塚崎 敦*

Physical Review Materials (Internet), 6(11), p.114203_1 - 114203_9, 2022/11

 被引用回数:5 パーセンタイル:34.44(Materials Science, Multidisciplinary)

Microscopic understanding of magnetization switching via domain nucleation and/or domain-wall propagation is fundamental knowledge for developing magnetic and spintronic devices. Here, we explore the underlying mechanism of the large coercivity of the magnetic Weyl semimetal Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ thin films, which is roughly ten times larger than that of Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ bulk single crystal, by measuring Hall resistance in constricted wire devices. The discretized steplike variations appear in the hysteresis loops of the Hall resistance in 0.6 micrometers wide and narrower devices, indicating that the size of the reversed magnetic domain is comparable to the active area of the Hall devices. By counting the number of discrete features, the average diameter of the reversed magnetic domain is estimated to be 80 nm. Individually, the diameter of the reversed domain nucleus is evaluated to be roughly 2 nm. Considering the difference in the diameters of the reversed magnetic domain and the reversed domain nucleus, we ascribed the large coercivity of the Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ thin films to a large nucleation field owing to the uniform crystallinity within grains and strong domain-wall pinning at grain boundaries specific to the thin films. With the large nucleation field in the films, an engineering of the domain-wall pinning sites is a promising approach to control the nucleation, manipulation, and detection of the single domain wall in Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ thin-film devices.

論文

Large antisymmetric interlayer exchange coupling enabling perpendicular magnetization switching by an in-plane magnetic field

増田 啓人*; 関 剛斎*; 山根 結太*; Modak, R.*; 内田 健一*; 家田 淳一; Lau, Y.-C.*; 深見 俊輔*; 高梨 弘毅

Physical Review Applied (Internet), 17(5), p.054036_1 - 054036_9, 2022/05

 被引用回数:9 パーセンタイル:59.76(Physics, Applied)

反対称層間交換結合(AIEC)が最近発見され、人工反強磁性体(SAF)の傾角磁化の誘起を通じた磁化スイッチングにおいて極めて重要な役割を果たしている。本研究では、くさび形の層を持つ垂直磁化多層膜Pt/Co/Ir/Co/Ptにおける大きなAIECを報告をする。AIECの有効磁場は、対称的な層間交換結合に関連しており、AIECを強化するための指針を提供する。SAFに対する拡張Stoner-Wohlfarthモデルを開発し、その磁化スイッチングの重要な要素を明らかにする。理論的知識と実験結果を組み合わせることで、面内磁場のみによる垂直磁化スイッチングが達成される。

論文

Magnetoelastic anisotropy in Heusler-type Mn$$_{2-delta}$$CoGa$$_{1+delta}$$ 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:7 パーセンタイル:46.06(Materials Science, Multidisciplinary)

This study focuses on an inverse-type Heusler alloy, Mn$$_{2-delta}$$CoGa$$_{1+delta}$$ (MCG), with a small off-stoichiometry ($$delta$$), showing perpendicular magnetic anisotropy (PMA). We observed a relatively large uniaxial magnetocrystalline anisotropy constant ($$K_mathrm{u}$$) on the order of 10$$^5$$ J/m$$^3$$ 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 $$K_mathrm{u}$$. 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 $$uparrow$$- and the unoccupied $$downarrow$$-spin states is responsible for the PMA of the MCG films.

論文

Microstructures and interface magnetic moments in Mn$$_{2}$$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:10.80(Chemistry, Multidisciplinary)

Heusler alloys exhibit various magnetic properties. In this study, a layered sample consisting of a Heusler alloy, Mn$$_{2}$$VAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered Mn$$_{2}$$VAl is known as a ferrimagnet, the Mn$$_{2}$$VAl/Fe layered structure exhibits exchange bias. The high-angle annular dark field STEM images demonstrated the formation of Mn$$_{2}$$VAl clusters with the L2$$_{1}$$ 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$$_{1}$$ phase and antiferromagnetic Mn-moments in the Mn$$_{2}$$VAl layer are important for the exchange bias.

論文

Evaluation of edge domains in giant magnetoresistive junctions

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:4.62(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$$_2$$O$$_3$$ on the sides of the GMR pillar. This generates a spin wave in Fe$$_2$$O$$_3$$, 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 $$(1.1pm0.1)times10^7$$ A/cm$$^2$$ to $$(7.0pm0.5)times10^7$$ A/cm$$^2$$. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be $$10%-15%$$ by spin-transfer torque.

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