面向SOT-MRAM应用的亚铁磁合金自旋旋转效应机理与调控

磁性材料具有时间反演对称破缺特性，理论上能够产生比非磁性材料更丰富的自旋轨道效应，比如自旋旋转效应。该效应首先在铁磁/非磁性界面处被发现，不同于自旋霍尔效应中偏置电场、自旋电流以及自旋极化方向相互正交的要求，自旋旋转效应犹如自旋霍尔效应产生的自旋绕磁矩旋转，从而得到不同的自旋极化取向。因此，利用自旋旋转效应可以产生垂直极化自旋，实现无场辅助垂直磁矩翻转过程，在自旋轨道力矩磁性随机存储器研究中有着重要应用价值。当前自旋旋转效应的物理形成机理还不明了，“电荷-旋转自旋”的转化效率还不高。本研究利用具有长自旋退相干长度的亚铁磁合金，重点对自旋旋转效应的体效应机制做深入探究，提出通过材料厚度与自旋退相干长度调控对自旋旋转效应进行效率优化与增强。同时，针对亚铁磁/非磁性/铁磁多层膜样品的自旋轨道力矩测试，提出磁光克尔效应与铁磁共振技术相结合的实验方法，以解决磁性多层膜的测试问题。

Ferromagnets have the property of time-reversal symmetry breaking, in which in principle can exhibit richer spin-orbit effects than in nonmagnets, for instance, the spin rotation effect. It’s been first demonstrated at the ferromagnet/nonmagnet interface. Compared to the spin Hall effect, which requires that bias electric field, spin current and spin orientation are all orthogonal to each other, the spin rotation effect behaves like the spin Hall effect induced spin is rotating about the magnetization. Its spin has quite different spin orientation. Thus, it can generate a spin with perpendicular spin polarization, which can be applied to the field-free perpendicularly magnetized layer switching process. This will have an important application in the SOT-MRAM. At present, the mechanism of the spin rotation effect is still not clear. Its “charge to rotated-spin” efficiency is low. In this study, we will focus on the research of bulk contribution from the spin rotation effect in ferrimagnetic alloys who can have a long spin dephasing length. We propose to optimize and enhance the efficiency of the spin rotation effect by manipulating a ferrimagnet thickness and spin dephasing length. Meanwhile, we develop a MOKE and FMR combined spin-orbit torque measurement technique for the ferrimagnet/nonmagnet/ferromagnet multilayer samples. We aim to overcome the difficult happening during the magnetic multilayer spin-orbit torque measurement.