Strong bias effect on voltage-driven torque at epitaxial Fe-MgO interface
Strong bias effect on voltage-driven torque at epitaxial Fe-MgO interface
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对外延 Fe-MgO 界面电压驱动扭矩的强偏置效应
DOI：
10.1103/physrevx.7.031018
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
and Y. Suzuki
中科院分区：
文献类型：
--
作者：
S. Miwa*;J. Fujimoto;P. Risius;K. Nawaoka;M. Goto;and Y. Suzuki
力矩可以通过电流和/或电压直接提供给纳米磁体中的磁化。这种技术可以在没有电磁感应的情况下实现电流(电压)到自旋的转换，并已被广泛研究用于存储器件。在各种力矩中，最近发现了自旋-轨道分裂引起的力矩。然而，由于面内电流器件具有相同的对称性，因此对体相关扭矩和界面相关扭矩的定量理解仍然缺乏。在这篇文章中，我们提出了纯界面相关的扭矩可以用电流垂直于平面隧道结的自旋扭矩铁磁共振来表征。制备了外延Fe-MgO-V隧道结来表征Fe-MgO处的界面相关扭矩。我们发现电流驱动的扭矩可以忽略不计，而电压驱动的扭矩随着氧化镁势垒厚度的减小而显著增加。获得的最大扭矩可达，可与的压控磁各向异性相媲美。电压驱动的转矩表现出很强的直流偏置-电压相关性，这是传统的压控磁各向异性所不能解释的。隧道各向异性磁电阻谱表明，扭矩与Fe-MgO的界面态有关。这种对磁性质的表面态敏感的电调制为界面磁性领域提供了新的见解。
Torque can be provided to magnetization in nanomagnets directly by electric current and/or voltage. This technique enables electric current (voltage)-to-spin conversion without electromagnetic induction, and has been intensively studied for memory device applications. Among the various kinds of torque, torque induced by spin-orbit splitting has recently been found. However, quantitative understanding of bulk-related torque and interface-related torque is still lacking because of their identical symmetry for current-in-plane devices. In this paper, we propose that a pure interface-related torque can be characterized by spin-torque ferromagnetic resonance with a current-perpendicular-to-plane tunnel junction. Epitaxial Fe-MgO-V tunnel junctions are prepared to characterize the interface-related torque at Fe-MgO. We find that the current-driven torque is negligible, and a significant enhancement of the voltage-driven torque is observed when the MgO barrier thickness decreases. The maximum torque obtained is as large as, which is comparable to the voltage-controlled magnetic anisotropy of. The voltage-driven torque shows strong dc-bias-voltage dependence that cannot be explained by conventional voltage-controlled magnetic anisotropy. Tunnel anisotropic magnetoresistance spectroscopy suggests that the torque is correlated to an interface state at the Fe-MgO. This surface-state-sensitive electric modulation of magnetic properties provides new insight into the field of interface magnetism.