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論文

Antiferromagnetic anisotropy determination by spin Hall magnetoresistance

Wang, H.*; Hou, D.*; Qiu, Z.*; 吉川 貴史*; 齊藤 英治; Jin, X.*

Journal of Applied Physics, 122(8), p.083907_1 - 083907_6, 2017/08

 被引用回数:2 パーセンタイル:14.14(Physics, Applied)

An electric method for measuring magnetic anisotropy in antiferromagnetic insulators (AFIs) is proposed. When a metallic film with strong spin-orbit interactions, e.g., platinum (Pt), is deposited on an AFI, its resistance should be affected by the direction of the AFI N$'e$el vector due to the spin Hall magnetoresistance (SMR). Accordingly, the direction of the AFI N$'e$el vector, which is affected by both the external magnetic field and the magnetic anisotropy, is reflected in resistance of Pt. The magnetic field angle dependence of the resistance of Pt on AFI is calculated by considering the SMR, which indicates that the antiferromagnetic anisotropy can be obtained experimentally by monitoring the Pt resistance in strong magnetic fields. Calculations are performed for realistic systems such as Pt/Cr$$_2$$O$$_3$$, Pt/NiO, and Pt/CoO.

論文

Origin of the spin Seebeck effect in compensated ferrimagnets

Gepr$"a$gs, S.*; Kehlberger, A.*; Coletta, F.*; Qiu, Z.*; Guo, E.-J.*; Schulz, T.*; Mix, C.*; Meyer, S.*; Kamra, A.*; Althammer, M.*; et al.

Nature Communications (Internet), 7, p.10452_1 - 10452_6, 2016/02

 被引用回数:100 パーセンタイル:97.17(Multidisciplinary Sciences)

Magnons are the elementary excitations of a magnetically ordered system. Here, we show that the spin Seebeck effect is sensitive to the complexities of the magnon spectrum. The spin Seebeck effect is caused by a thermally excited spin dynamics that is converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the spin Seebeck effect in the ferrimagnet gadlinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that high-energy exchange magnons play a key role in the spin Seebeck effect.

口頭

Elastoplastic deformation behavior of textured high strength steel after hydrogen charging studied by neutron diffraction

徐 平光; 石島 暖大; Qiu, H.*

no journal, , 

For ultrahigh strength steels, the hydrogen absorption from the environment may cause the hydrogen embrittlement (HE) phenomenon at a service loading much less than the nominal yield strength. Since HE has higher Charpy impacting susceptibility along RD (rolling direction) than along TD (transverse direction) in cold rolled steels, effects of texture and hydrogen charging on elastoplastic deformation of high strength steel plates are valuable to be investigated. In our research, though all the hydrogen-charged samples show typical ductile fracture characteristics in the macroscopic morphology, their total elongation and reduction in area decease to a certain content compared with the corresponding non-charged samples, e.g. 12% and 53% (hydrogen-charged RD sample) vs 15% and 65% (non-charged RD sample), confirming the occurrence of HE phenomenon. Generally, the tensile deformation of high strength steel with BCC crystal structure leads to the formation of $$<$$110$$>$$ fiber texture, and the large tensile strain means a higher integrated intensity ratio I$$_{110}$$/I$$_{211}$$ in the axial neutron diffraction pattern. It is interesting that the axial neutron pattern acquired from the necking fracture part of hydrogen-charged RD sample has a higher integrated intensity ratio than the corresponding necking fracture part of non-charged RD sample suggesting that the hydrogen charging accelerates the formation of $$<$$110$$>$$ fiber texture.

口頭

中性子回折法を用いた集合組織を有する高張力鋼板の水素脆化挙動評価

徐 平光; 石島 暖大; Qiu, H.*; 諸岡 聡; Harjo, S.

no journal, , 

最近の陽電子消滅法や水素マイクロプリント法など分析技術の進歩により、金属組織に対応した水素分布の可視化や存在位置まで検出できるようになった。一方で、水素脆化という力学特性の劣化進行過程に対して、原子レベルでの組織評価とマクロな機械試験を組み合わせた中性子回折技術が有効である。通常の回折法では、ppmレベルの拡散水素を含有した鉄鋼材料の結晶構造の変化を評価することは困難である。しかし、その鉄鋼材料の力学特性が拡散水素の影響を受けることに着目して、中性子回折法によるその場測定を用いて、水素チャージした高張力鋼板の水素脆化挙動と結晶回転を同時に評価した。水素チャージの有無に関係なく、引張変形の進行に伴い$$<$$110$$>$$結晶配向が強くなり、一方で$$<$$200$$>$$,$$<$$211$$>$$は弱くなった。これは単軸引張変形による結晶回転に由来する。$$<$$110$$>$$結晶配向は、ネッキング変形中にさらに強くなるが、その後、水素チャージなしの試料では、$$<$$110$$>$$結晶配向の緩和によって高い絞り率で破断に至ったのに対し、水素チャージした試料では、充分緩和せずに低い絞り率で破断に至った。

口頭

Effect of hydrogen charging on anisotropic tensile deformation behavior of high strength steel plate

徐 平光; 石島 暖大; Qiu, H.*; 諸岡 聡; Gong, W.*; Harjo, S.

no journal, , 

Hydrogen-induced ductility loss or hydrogen embrittlement is related to the diffusional entrance of environmental hydrogen into ultrahigh strength steel materials. Neutron diffraction as a powerful nondestructive method has been developed well for monitoring the elastoplastic deformation and the crystallographic texture evolution. However, considering the tiny amount of diffusive hydrogen on crystal structure of steel materials, the monitoring using neutron diffraction is thought as a challenging research. Neutron diffraction during tensile deformation of cylinder samples prepared from a 12mm-thick high strength steel plate with and without hydrogen charging was carried out in situ, and the grain orientation rotations were discussed through the relative change of normalized integration intensity of individual diffraction peaks. The anisotropy of elastoplastic deformation behaviors of high strength steel plate and the effect of hydrogen charging on total elongation and reduction in the area has been confirmed. $$<$$110$$>$$-fiber preferred orientation becomes stronger during uniaxial tensile deformation of samples with and without hydrogen charging; the complex multiaxial stress field during local necking deformation induces more evident weakening of final $$<$$110$$>$$-fiber preferred orientation in the non-hydrogen steel than the hydrogen charged steel, suggesting that neutron diffraction is suitable for monitoring the plastic deformation of hydrogen-charged high strength steel.

口頭

Neutron diffraction texture evaluation of hydrogen charged high strength steel after uniaxial tensile deformation

徐 平光; 石島 暖大; Qiu, H.*; 諸岡 聡; Gong, W.*; 川崎 卓郎; Harjo, S.

no journal, , 

High strength steels for pipelines and high-pressure vessels are susceptible to hydrogen embrittlement (HE), which is typically characterized by a loss of tensile ductility. In addition to the conventional factors including microstructure, hydrogen content, strain rate, temperature, and residual stress, the crystallographic texture has recently been reported to affect the HE susceptibility of steel plates. Here, the anisotropic tensile deformation behaviors and the texture evolution were comparably evaluated by using hydrogen-charged and non-charged tensile samples to investigate the mutual effect of texture and hydrogen charging. The changes in normalized diffraction intensities show that $$<$$110$$>$$//RD (RD: rolling direction) preferred orientation becomes stronger during the RD tensile deformation of hydrogen-charged and non-charged samples; the multiaxial stress field during necking deformation induces more evident weakening of final $$<$$110$$>$$//RD preferred orientation in the non-hydrogen steel. It suggests that the in situ neutron diffraction is suitable to monitor the plastic deformation behavior of hydrogen-charged high strength steel. Moreover, during the RD extension, $$<$$110$$>$$//RD texture component becomes strong and the $$<$$200$$>$$//TD$$sim$$$$<$$200$$>$$//ND components (TD: transverse direction; ND: normal direction) have a uniform pole density distribution, and the hydrogen charging accelerates the formation of this distribution. During the TD extension, $$<$$110$$>$$//TD component becomes strong, $$<$$200$$>$$//ND component disperses towards the circular direction 60$$^{circ}$$-tilted from ND, and the hydrogen charging accelerates such grain rotations. The appearance of higher maximum pole density of (200) pole figure shows good correspondence to lower uniform ductility of hydrogen-charged TD sample.

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