Catalan Institute of Nanoscience and Nanotechnology (ICN2), E-08193 Barcelona, Spain.
Nat Nanotechnol. 2013 Aug;8(8):587-93. doi: 10.1038/nnano.2013.145. Epub 2013 Jul 28.
Recent demonstrations of magnetization switching induced by in-plane current injection in heavy metal/ferromagnetic heterostructures have drawn increasing attention to spin torques based on orbital-to-spin momentum transfer. The symmetry, magnitude and origin of spin-orbit torques (SOTs), however, remain a matter of debate. Here we report on the three-dimensional vector measurement of SOTs in AlOx/Co/Pt and MgO/CoFeB/Ta trilayers using harmonic analysis of the anomalous and planar Hall effects. We provide a general scheme to measure the amplitude and direction of SOTs as a function of the magnetization direction. Based on space and time inversion symmetry arguments, we demonstrate that heavy metal/ferromagnetic layers allow for two different SOTs having odd and even behaviour with respect to magnetization reversal. Such torques include strongly anisotropic field-like and spin transfer-like components, which depend on the type of heavy metal layer and annealing treatment. These results call for SOT models that go beyond the spin Hall and Rashba effects investigated thus far.
最近，在重金属/铁磁异质结构中通过面内电流注入诱导磁化翻转的演示引起了人们对基于轨道到自旋动量转移的自旋扭矩的极大关注。然而，自旋轨道扭矩（SOT）的对称性、大小和起源仍然存在争议。在这里，我们使用反常霍尔效应和平面霍尔效应的谐波分析报告了在 AlOx/Co/Pt 和 MgO/CoFeB/Ta 三层膜中 SOT 的三维矢量测量。我们提供了一种一般的方案，可根据磁化方向测量 SOT 的幅度和方向。基于空间和时间反演对称性的论证，我们证明重金属/铁磁层允许两种不同的 SOT，它们相对于磁化反转具有奇数和偶数行为。这些扭矩包括强烈各向异性的场状和自旋转移状分量，它们取决于重金属层的类型和退火处理。这些结果要求超越迄今为止研究的自旋霍尔和 Rashba 效应的 SOT 模型。
