Study on FeCr thin film for a spintronic material with negative spin polarization
Study on FeCr thin film for a spintronic material with negative spin polarization
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DOI：
10.1016/j.jmmm.2022.169474
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发表时间：
2022-05
影响因子：
2.7
通讯作者：
H. Suto;T. Nakatani;Y. Kota;Asam Nagarjuna;H. Iwasaki;K. Amemiya;T. Mitsui;S. Sakai;Songtian Li;Y. Sakuraba
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文献类型：
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作者：
H. Suto;T. Nakatani;Y. Kota;Asam Nagarjuna;H. Iwasaki;K. Amemiya;T. Mitsui;S. Sakai;Songtian Li;Y. Sakuraba
负自旋极化材料产生自旋电流，其自旋方向与磁化方向相反。这一特性在技术上很重要，因为它增加了自旋电子器件设计的自由度。在本文中，我们从能带结构、原子磁矩和局域原子排列的角度研究了FeCr，以探索其作为负自旋极化材料的潜力。对无序 FeCr 合金的第一性原理计算预测了高负自旋极化，这归因于少数自旋的能带匹配。我们通过溅射沉积实验制备了 Cr 浓度 (x) 范围为 0.2 至 0.4 的 Fe1-xCrx 薄膜，并使用电流垂直于平面的巨磁阻 (GMR) 器件演示了逆磁阻，这提供了负自旋极化的证据。根据 GMR 装置测量估算出 Fe0.7Cr0.3 的自旋极化为 -0.28，低于计算值。同步加速器 X 射线磁圆二色性测量显示 Fe 和 Cr 磁矩的亚铁磁性配置。 Fe力矩在较宽的Cr浓度范围内表现出较大的力矩，而Cr力矩随着Cr浓度的增加而减小，这与计算结果一致。同步加速器穆斯堡尔光谱测量表明，即使在沉积状态下，FeCr 成分也存在不均匀性。退火后形成富Fe区域，反映了Fe-Cr体系的相分离性质。计算中没有考虑不均匀性，并且可能是实验中观察到的较小负自旋极化的根源。
Negative spin polarization materials generate a spin current whose spin direction is opposite to the magnetization direction. This characteristic is technologically important because it increases the freedom in the design of spintronic devices. In this paper, we studied FeCr from the viewpoints of band structure, atomic magnetic moments, and local atomic arrangement to explore its potentiality as a negative spin polarization material. First-principles calculations on the disordered FeCr alloy predicted a high negative spin polarization, which was attributed to the band matching of the minority spin. We experimentally fabricated Fe1-xCrxthin films in the Cr concentration (x) range from 0.2 to 0.4 by sputter deposition and demonstrated inverse magnetoresistance using current-perpendicular-to-plane giant magnetoresistance (GMR) devices, which provided evidence of negative spin polarization. The spin polarization of Fe0.7Cr0.3estimated from the GMR device measurements was −0.28 and fell below the calculated value. Synchrotron X-ray magnetic circular dichroism measurements showed a ferrimagnetic configuration of the Fe and Cr magnetic moments. The Fe moment showed a large moment over a wide Cr concentration range, whereas the Cr moment decreased with the Cr concentration, which agreed with the calculation result. Synchrotron Mössbauer spectroscopy measurements indicated the inhomogeneity of the FeCr composition even in the as-deposited state. Fe-rich regions were formed after annealing, reflecting the phase separation nature of the Fe-Cr system. Inhomogeneity was not considered in the calculation and could be the origin of the smaller negative spin polarization observed in the experiment.