検索対象:     
報告書番号:
※ 半角英数字
 年 ~ 
 年
検索結果: 39 件中 1件目~20件目を表示

発表形式

Initialising ...

選択項目を絞り込む

掲載資料名

Initialising ...

発表会議名

Initialising ...

筆頭著者名

Initialising ...

キーワード

Initialising ...

使用言語

Initialising ...

発行年

Initialising ...

開催年

Initialising ...

選択した検索結果をダウンロード

論文

Enhanced magneto-optical Kerr effect at Fe/insulator interfaces

Gu, B.; 高橋 三郎*; 前川 禎通

Physical Review B, 96(21), p.214423_1 - 214423_6, 2017/12

AA2017-0686.pdf:0.45MB

 被引用回数:6 パーセンタイル:41.1(Materials Science, Multidisciplinary)

Using density functional theory calculations, we have found an enhanced magneto-optical Kerr effect in Fe/insulator interfaces. The results of our study indicate that interfacial Fe atoms in the Fe films have a lowdimensional nature, which causes the following two effects: (1) The diagonal component $$sigma_{xx}$$ of the optical conductivity decreases dramatically because the hopping integral for electrons between Fe atoms is suppressed by the low dimensionality. (2) The off-diagonal component $$sigma_{xy}$$ of the optical conductivity does not change at low photon energies, but it is enhanced at photon energies around 2 eV, where we obtain enhanced orbital magnetic moments and spin-orbit correlations for the interfacial Fe atoms. A large Kerr angle develops in proportion to the ratio $$sigma_{xy}$$/$$sigma_{xx}$$. Our findings indicate an efficient way to enhance the effect of spin-orbit coupling at metal/insulator interfaces without using heavy elements.

論文

Enhanced orbital magnetic moment in FeCo nanogranules observed by Barnett effect

緒方 裕大; 中堂 博之; Gu, B.; 小林 伸聖*; 小野 正雄; 針井 一哉; 松尾 衛; 齊藤 英治; 前川 禎通

Journal of Magnetism and Magnetic Materials, 442, p.329 - 331, 2017/11

 被引用回数:5 パーセンタイル:57.14(Materials Science, Multidisciplinary)

The gyroscopic g factor, $$g'$$, of FeCo nanogranules embedded in a matrix of MgF$$_2$$ (FeCo-MgF$$_2$$) was determined by measuring the magnetic-field generation from a rotating sample due to the Barnett effect. The $$g'$$ value of the FeCo-MgF$$_2$$ is estimated to be 1.76 $$pm$$ 0.11. The orbital contribution to the magnetic moment in the FeCo nanogranules was found to be quite large compared with that in bulk FeCo, being consistent with a density-functional-theory calculation that shows that the orbital magnetic moment may increase at the FeCo/MgF$$_2$$ interfaces. The result suggests that the orbital magnetic moment is enhanced by symmetry breaking at the surface of the FeCo nanogranules.

論文

New p- and n-type ferromagnetic semiconductors; Cr-doped BaZn$$_{2}$$As$$_{2}$$

Gu, B.; 前川 禎通

AIP Advances (Internet), 7(5), p.055805_1 - 055805_6, 2017/05

 被引用回数:3 パーセンタイル:21.37(Nanoscience & Nanotechnology)

We find new ferromagnetic semiconductors, Cr-doped BaZn$$_{2}$$As$$_{2}$$, by employing a combined method of the density functional theory and the quantum Monte Carlo simulation. Due to a narrow band gap of 0.2 eV in host BaZn$$_{2}$$As$$_{2}$$ and the different hybridization of 3d orbitals of Cr impurity, the impurity bound states have been induced both below the top of valence band and above the bottom of conduction band. The long-range ferromagnetic coupling between Cr impurities is obtained with both p- and n-type carriers.

論文

Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy

岡田 篤*; He, S.*; Gu, B.; 金井 駿*; Soumyanarayanan, A.*; Lim, S. T.*; Tran, M.*; 森 道康; 前川 禎通; 松倉 文礼*; et al.

Proceedings of the National Academy of Sciences of the United States of America, 144(15), p.3815 - 3820, 2017/04

Studies of magnetization dynamics have incessantly facilitated the discovery of fundamentally novel physical phenomena, making steady headway in the development of magnetic and spintronics devices. The dynamics can be induced and detected electrically, offering new functionalities in advanced electronics at the nanoscale. However, its scattering mechanism is still disputed. Understanding the mechanism in thin films is especially important, because most spintronics devices are made from stacks of multilayers with nanometer thickness. The stacks are known to possess interfacial magnetic anisotropy, a central property for applications, whose influence on the dynamics remains unknown. Here, we investigate the impact of interfacial anisotropy by adopting CoFeB/MgO as a model system. Through systematic and complementary measurements of ferromagnetic resonance (FMR) on a series of thin films, we identify narrower FMR linewidths at higher temperatures. We explicitly rule out the temperature dependence of intrinsic damping as a possible cause, and it is also not expected from existing extrinsic scattering mechanisms for ferromagnets. We ascribe this observation to motional narrowing, an old concept so far neglected in the analyses of FMR spectra. The effect is confirmed to originate from interfacial anisotropy, impacting the practical technology of spin-based nanodevices up to room temperature.

論文

Skew scattering from correlated systems; Impurities and collective excitations in the spin Hall effect

Ziman, T.*; Gu, B.; 前川 禎通

Journal of the Physical Society of Japan, 86(1), p.011005_1 - 011005_8, 2017/01

 被引用回数:1 パーセンタイル:15.72(Physics, Multidisciplinary)

We examine the enhancement of the spin Hall effect due to resonant skew scattering induced by electron correlations. For single-impurity scattering, local Coulomb correlations may significantly change the observed spin Hall angle. There may be additional effects because of the special atomic environment close to a surface: extra degeneracies compared to the bulk, enhanced correlations that move the relative $$d$$- or $$f$$-levels, and interference effects coming from the lower local dimension. Our results may explain the very large spin Hall angle observed in CuBi alloys. We discuss the impact on the spin Hall effect from cooperative effects, firstly in an itinerant ferromagnet where there is an anomaly near the Curie temperature originating from high-order spin fluctuations. The second case considered is a metallic spin glass, where exchange via slowly fluctuating magnetic moments may lead to the precession of an injected spin current.

論文

Diluted magnetic semiconductors with narrow band gaps

Gu, B.; 前川 禎通

Physical Review B, 94(15), p.155202_1 - 155202_8, 2016/10

AA2016-0395.pdf:0.38MB

 被引用回数:16 パーセンタイル:68.78(Materials Science, Multidisciplinary)

The diluted magnetic semiconductors (DMSs) have received considerable attention owing to potential applications based on the use of both charge and spin degrees of freedom in electronic devices. Historically, (Ga,Mn)As has received the most attention in DMSs, and so far the highest Curie temperature in (Ga,Mn)As has been $$T_{c}$$ = 190 K in the experiment. The substitution of divalent Mn atoms into trivalent Ga sites introduces hole carriers; thus, (Ga,Mn)As is a $$p$$-type DMS. Here, we propose a method to realize DMSs with $$p$$- and $$n$$-type carriers by choosing host semiconductors with a narrow band gap. By employing a combination of the density function theory and quantum Monte Carlo simulation, we demonstrate such semiconductors using Mn-doped BaZn$$_{2}$$As$$_{2}$$, which has a band gap of 0.2 eV. In addition, we found a nontoxic DMS Mn-doped BaZn$$_{2}$$Sb$$_{2}$$, of which the Curie temperature $$T_{c}$$ is predicted to be higher than that of Mn-doped BaZn$$_{2}$$As$$_{2}$$, the $$T_{c}$$ of which was up to 230 K in a recent experiment.

論文

What determines the sign of the spin Hall effects in Cu alloys doped with 5d elements?

Xu, Z.; Gu, B.; 森 道康; Ziman, T.*; 前川 禎通

Journal of Magnetism and Magnetic Materials, 400, p.184 - 187, 2016/02

 被引用回数:3 パーセンタイル:20.49(Materials Science, Multidisciplinary)

We perform a systematical analysis of the spin Hall effect (SHE) in the Cu alloys doped with a series of 5d elements, by the combined approach of density functional theory and Hartree-Fock approximation. We find that not only the spin orbit interactions (SOI) in both the 5d and 6p orbitals, but also the local correlations in the 5d orbitals of the impurities, are decisive on the sign of the spin Hall angle (SHA). Including all of these three factors properly, we predict the SHA for each alloy in the series. The signs of CuIr and CuPt are sensitive to perturbation of the local correlations. This observation is favorable for controlling the sign of the transverse spin Hall voltage.

論文

Strong suppression of the spin hall effect in the spin glass state

新見 康洋*; 木俣 基*; 大森 康智*; Gu, B.; Ziman, T.*; 前川 禎通; Fert, A.*; 大谷 義近*

Physical Review Letters, 115(19), p.196602_1 - 196602_5, 2015/11

 被引用回数:11 パーセンタイル:66.4(Physics, Multidisciplinary)

We have measured spin Hall effects in spin glass metals, CuMnBi alloys, with the spin absorption method in the lateral spin valve structure. Far above the spin glass temperature $$T_{g}$$ where the magnetic moments of Mn impurities are randomly frozen, the spin Hall angle of a CuMnBi ternary alloy is as large as that of a CuBi binary alloy. Surprisingly, however, it starts to decrease at about 4$$T_{g}$$ and becomes as little as 7 times smaller at 0.5$$T_{g}$$. A similar tendency was also observed in anomalous Hall effects in the ternary alloys. We propose an explanation in terms of a simple model considering the relative dynamics between the localized moment and the conduction electron spin.

論文

Enhanced spin Hall effect by electron correlations in CuBi alloys

Gu, B.; Xu, Z.; 森 道康; Ziman, T.*; 前川 禎通

Journal of Applied Physics, 117(17), p.17D503_1 - 17D503_4, 2015/05

 被引用回数:6 パーセンタイル:32.7(Physics, Applied)

We find that the SHA can be dramatically enhanced by Bi impurities close to the Cu surface. The mechanisms of this enhancement are two-fold. One is that the localized impurity state on surface has a decreased hybridization and combined with Coulomb correlation effect. The other comes from the low-dimensional state of conduction electrons on surface, which results in a further enhancement of skew scattering by impurities. Furthermore, we note that a discrepancy in sign of SHA between the experiment and previous theories is simply caused by different definitions of SHA. This re-establishes skew scattering as the essential mechanism underlying the spin Hall effect in CuBi alloys.

論文

Analysis of the spin Hall effect in CuIr alloys; Combined approach of density functional theory and Hartree-Fock approximation

Xu, Z.; Gu, B.; 森 道康; Ziman, T.*; 前川 禎通

Journal of Applied Physics, 117(17), p.17D510_1 - 17D510_4, 2015/05

 被引用回数:4 パーセンタイル:22.79(Physics, Applied)

We analyze the spin Hall effect in CuIr alloys in theory by the combined approach of the density functional theory (DFT) and Hartree-Fock (HF) approximation. The spin Hall angle (SHA) is obtained to be negative without the local correlation effects. After including the local correlation effects of the 5$$d$$ orbitals of Ir impurities, the SHA becomes positive with realistic correlation parameters and consistent with experiment. Moreover, our analysis shows that the DFT + HF approach is a convenient and general method to study the influence of local correlation effects on the spin Hall effect.

論文

Charge-to-spin conversion and spin diffusion in Bi/Ag bilayers observed by spin-polarized positron beam

Zhang, H. J.; 山本 春也; Gu, B.; Li, H.; 前川 雅樹; 深谷 有喜; 河裾 厚男

Physical Review Letters, 114(16), p.166602_1 - 166602_5, 2015/04

 被引用回数:38 パーセンタイル:89.02(Physics, Multidisciplinary)

スピン偏極陽電子ビームを用いた最表面ポジトロニウム消滅過程の観測を通じて、Bi/Ag二層膜中のラシュバ-エデルシュタイン効果に伴う電荷-スピン変換の直接検出に初めて成功した。同一の通電方向に対して、BiとAgの表面では逆のスピン偏極が得られた。スピン偏極率は、膜の厚さが増すとともに指数関数的に減少することが知られた。以上の結果は、Bi/Ag界面で生成したスピンが、両層を通じて最表面に伝導・蓄積することを示している。

論文

Sign change of the spin Hall effect due to electron correlation in nonmagnetic CuIr alloys

Xu, Z.; Gu, B.; 森 道康; Ziman, T.*; 前川 禎通

Physical Review Letters, 114(1), p.017202_1 - 017202_5, 2015/01

 被引用回数:15 パーセンタイル:73.28(Physics, Multidisciplinary)

Recently a positive spin Hall angle (SHA) of 0.021, was observed experimentally in nonmagnetic CuIr alloys and attributed predominantly to an extrinsic skew scattering mechanism, while a negative SHA was obtained from ab initio calculations, using consistent definitions of the SHA. We reconsider the SHA in CuIr alloys, with the effects of the local electron correlation U in 5d orbitals of Ir impurities, included by the quantum Monte Carlo method. We found that the SHA is negative if we ignore such local electron correlation, but becomes positive once U approaches a realistic value. This may open up a way to control the sign of the SHA by manipulating the occupation number of impurities.

論文

Negatively charged muonium as a detector of electron spin polarization; A Puzzle and a possible theory

Gu, B.; Ziman, T.*; 前川 禎通

JPS Conference Proceedings (Internet), 2, p.010301_1 - 010301_5, 2014/03

We explore theoretical explanations for laser pumped experiments, that have established that muonium can be a tool in spintronics for following non-equilibrium spin polarizations of the conduction electrons. In the original experiments on Si the sensitivity was argued to be due to spin exchange with the bound electron in muonium, but in GaAs an effect is seen even in the case of negatively charged muonium. This is more problematic, as spin exchange with a third electron should be weak given the spin singlet state of the two bound electrons of the negative muonium ion. We discuss a mechanism to explain the sensitivity of negatively charged muonium ions to the spin-polarization of semiconductors in terms of the coherent mixing of charge states induced by hybridization with the semiconducting host.

論文

Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping

Deng, Z.*; Zhao, K.*; Gu, B.; Han, W.*; Zhu, J. L.*; Wang, X. C.*; Li, X.*; Liu, Q. Q.*; Yu, R. C.*; 後神 達郎*; et al.

Physical Review B, 88(8), p.081203_1 - 081203_5, 2013/08

 被引用回数:66 パーセンタイル:92.87(Materials Science, Multidisciplinary)

We report the discovery of a diluted magnetic semiconductor, Li(Zn,Mn)P, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn$$^{2+}$$ for Zn$$^{2+}$$, respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a ${it p}$-type ferromagnetic semiconductor with excess lithium providing charge doping. First-principles calculations indicate that excess Li is favored to partially occupy the Zn site, leading to hole doping. Ferromagnetism with Curie temperature up to 34 K is achieved while the system still shows semiconducting transport behavior.

論文

Anisotropic two-dimensional electron gas at the LaAlO$$_{3}$$/SrTiO$$_{3}$$ (110) interface

Annadi, A.*; Zhang, Q.*; Renshaw Wang, X.*; Tuzla, N.*; Gopinadhan, K.*; L$"u$, W. M.*; Roy Barman, A.*; Liu, Z. Q.*; Srivastava, A.*; Saha, S.*; et al.

Nature Communications (Internet), 4, p.1838_1 - 1838_7, 2013/05

 被引用回数:84 パーセンタイル:94.96(Multidisciplinary Sciences)

We report the observation of unexpected conductivity at the LaAlO$$_{3}$$/SrTiO$$_{3}$$ interface prepared on (110)-oriented SrTiO$$_{3}$$, with a LaAlO$$_{3}$$-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO$$_{2}$$/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

論文

Theory of the spin Hall effect, and its inverse, in a ferromagnetic metal near the Curie temperature

Gu, B.; Ziman, T.*; 前川 禎通

Physical Review B, 86(24), p.241303_1 - 241303_5, 2012/12

 被引用回数:10 パーセンタイル:45.04(Materials Science, Multidisciplinary)

We give a theory of the inverse spin Hall effect (ISHE) in ferromagnetic metals based on skew scattering via collective spin fluctuations. This extends Kondo's theory of the anomalous Hall effect (AHE) to include short-range spin-spin correlations. We find a relation between the ISHE and the four-spin correlations near the Curie temperature $$T$$$$_{rm c}$$. Such four-spin correlations do not contribute to the AHE, which relates to the three-spin correlations. Thus our theory shows an essential difference between the AHE and ISHE, providing an essential complement to Kondo's classic theory of the AHE in metals. We note the relation to skew-scattering mechanisms based on impurity scattering. Our theory can be compared to recent experimental results by Wei et al. for the ISHE in ferromagnetic alloys.

論文

The Spin Hall effect as a probe of nonlinear spin fluctuations

Wei, D. H.*; 新見 康洋*; Gu, B.; Ziman, T.*; 前川 禎通; 大谷 義近*

Nature Communications (Internet), 3, p.1058_1 - 1058_5, 2012/09

 被引用回数:26 パーセンタイル:78.59(Multidisciplinary Sciences)

The spin Hall effect (SHE) and its inverse have key roles in spintronic devices as they allow conversion of charge currents to and from spin currents. The conversion efficiency strongly depends on material details, such as the electronic band structure and the nature of impurities. Here we show an anomaly in the inverse SHE in weak ferromagnetic NiPd alloys near their Curie temperatures with a shape independent of material details, such as Ni concentrations. By extending Kondo's model for the anomalous Hall effect (AHE), we explain the observed anomaly as originating from the second-order nonlinear spin fluctuation of Ni moments. This brings to light an essential symmetry difference between the SHE and the AHE, which reflects the first-order nonlinear fluctuations of local moments. Our finding opens up a new application of the SHE, by which a minuscule magnetic moment can be detected.

論文

Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor

Deng, Z.*; Jin, C. Q.*; Liu, Q. Q.*; Wang, X. C.*; Zhu, J. L.*; Feng, S. M.*; Chen, L. C.*; Yu, R. C.*; Arguello, C.*; 後神 達郎*; et al.

Nature Communications (Internet), 2, p.1425_1 - 1425_5, 2011/08

 被引用回数:137 パーセンタイル:93.89(Multidisciplinary Sciences)

(Ga,Mn)Asは典型的な強磁性III-V族半導体として知られている。これは3価のGa原子を2価のMnで置き換えたものであるが、化学的溶解度が限られているため準安定であり、薄膜でしか製作できないものであった。また電子ドープも行うことができなかった。この困難な条件を超えるため、Masekらは理論的にI-II-V族半導体LiZnAsを提案した。この物質では原子価が等しい(Zn,Mn)の置き換えによる磁性の発現とLi濃度を過剰あるいは不足させることによるキャリアードープを独立に制御可能である。本研究では世界で初めてバルクな状態でのLi$$_{1+y}$$(Zn$$_{1-x}$$Mn$$_x$$)Asの合成に成功した。わずかにLiを過剰にすることで、50Kまでの温度で強磁性が現れること、またp型のキャリアーを持つことが観測され、これらの結果を報告した。

論文

Giant spin Hall effect of Au films with Pt impurities; Surface-assisted skew scattering

Gu, B.; Ziman, T.*; Guo, G.-Y.*; 永長 直人; 前川 禎通

Journal of Applied Physics, 109(7), p.070502_1 - 070502_3, 2011/03

表面で発生するスキュー散乱の効果を考えることにより、室温で巨大なスピンホール効果が現れることを理論的に示した。密度汎関数理論と量子モンテカルロ法を組合せ、さまざまな金の中におけるプラチナ不純物によるスピンホール効果を調べた。バルクの金ではスピンホール角は小さいにもかかわらず、金の(111)面において、スピンホール角が0.1よりも大きくなりうること、また金(001)面上では約半分に減少することを示した。この量子モンテカルロによる結果は、プラチナ不純物のスピン軌道相互作用が金の(001)面と(111)面において増大していることを示している。この現象は、プラチナの5dレベルは電荷ゆらぎによってフェルミレベルまで上昇するため、加えてバルクの金や金(001)面上においてはプラチナに対して1つのチャンネルだけであるが、金(111)面上では、2つのチャンネルが存在するために生じることを明らかにした。

論文

Surface-assisted spin Hall effect in Au films with Pt impurities

Gu, B.; 管井 勇*; Ziman, T.*; Guo, G. Y.*; 永長 直人; 関 剛斎*; 高梨 弘毅; 前川 禎通

Physical Review Letters, 105(21), p.216401_1 - 216401_4, 2010/11

 被引用回数:63 パーセンタイル:90.42(Physics, Multidisciplinary)

We show, both experimentally and theoretically, a novel route to obtain giant room temperature spin Hall effect due to surface-assisted skew scattering. In the experiment, we report the spin Hall effect in Pt-doped Au films with different thicknesses $$t_N$$. The giant spin Hall angle $$gamma_S$$ = $$0.12 pm 0.04$$ is obtained for $$t_N$$ = 10 nm at room temperature, while it is much smaller for $$t_N$$ = 20 nm sample. Combined ${it ab initio}$ and quantum Monte Carlo calculations for the skew scattering due to a Pt impurity show $$gamma_S$$ $$cong$$ 0.1 on the Au (111) surface, while it is small in bulk Au. The quantum Monte Carlo results show that the spin-orbit interaction of the Pt impurity on the Au (111) surface is enhanced, because the Pt 5$$d$$ levels are lifted to the Fermi level due to the valence fluctuation. In addition, there are two spin-orbit interaction channels on the Au (111) surface, while only one in bulk Au.

39 件中 1件目~20件目を表示