Spin torque nano-oscillators with a perpendicular spin polarizer
Spin torque nano-oscillators with a perpendicular spin polarizer
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具有垂直自旋偏振器的自旋扭矩纳米振荡器
DOI：
10.1088/1674-1056/28/3/037503
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发表时间：
2019
影响因子：
1.7
通讯作者：
Liu Yaowen
中科院分区：
文献类型：
--
作者：
Zheng Cuixiu;Chen Hao Hsau;Zhang Xiangli;Zhang Zongzhi;Liu Yaowen
本文综述了自旋转移矩纳米振荡器（STNO）器件中自旋转移矩（STT）诱导磁化动力学的研究进展。STNO包含面内（IP）磁化自由层和面外（OP）磁化自旋极化层。在简要介绍之后，我们首先使用介观微磁模拟，其基于包括STT效应的Landau-Lifshitz-吉尔伯特方程，来指定自旋扭矩项如何可以调谐自由层的磁化进动轨道，示出振荡器频率与电流密度和自由层磁化的z分量成比例。接下来，我们提出了一个类似的巨旋近似的模型来描述这种类型的STNO的动力学性质。在此基础上，我们进一步研究了IP和OP双自旋极化器激发的STNO的进动动力学。数值模拟和理论分析都表明，旋进频率只与OP偏振器的自旋力矩成线性关系，而与IP偏振器的自旋力矩无关。最后介绍了一种从实验坐标系到旋转坐标系的坐标变换方法，从而将非平稳OP磁化进动过程变换为旋转坐标系下的平稳过程。通过这种方法，提出了一种很有前途的数字移频键控调制技术，它可以很好地控制磁化进动在给定的轨道上，并且可以通过自旋极化电流和磁场（或电场）脉冲的共同作用来调节其进动频率。
We present an overview in the understanding of spin-transfer torque (STT) induced magnetization dynamics in spin-torque nano-oscillator (STNO) devices. The STNO contains an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized spin polarizing layer. After a brief introduction, we first use mesoscopic micromagnetic simulations, which are based on the Landau–Lifshitz–Gilbert equation including the STT effect, to specify how a spin-torque term may tune the magnetization precession orbits of the free layer, showing that the oscillator frequency is proportional to the current density and the z-component of the free layer magnetization. Next, we propose a pendulum-like model within the macrospin approximation to describe the dynamic properties in such type of STNOs. After that, we further show the procession dynamics of the STNOs excited by IP and OP dual spin-polarizers. Both the numerical simulations and analytical theory indicate that the precession frequency is linearly proportional to the spin-torque of the OP polarizer only and is irrelevant to the spin-torque of the IP polarizer. Finally, a promising approach of coordinate transformation from the laboratory frame to the rotation frame is introduced, by which the nonstationary OP magnetization precession process is therefore transformed into the stationary process in the rotation frame. Through this method, a promising digital frequency shift-key modulation technique is presented, in which the magnetization precession can be well controlled at a given orbit as well as its precession frequency can be tuned with the co-action of spin polarized current and magnetic field (or electric field) pulses.