自旋转移力矩装置中的回跳现象、可能的原因及对策
Back hopping in spin-transfer-torque devices, possible origin and counter measures
摘要：
利用自旋扩散模型研究了磁性多层膜系统中不期望的高频自由层开关效应，即背跳效应。一个可能的起源的回跳效应被发现是不稳定的钉扎层，导致永久切换的两个层。通过微磁学模拟得到了不同材料参数对自由层和钉扎层临界开关电流的影响。发现选择具有低极化$β$和饱和磁化强度$M_s$的自由层材料以及具有高$β$和$M_s$的钉扎层材料导致低自由层临界电流和高钉扎层临界电流，并且因此降低了回跳的可能性。虽然在各种类型的设备中观察到反向跳跃，但只有很少的实验在垂直磁化系统中表现出这种效应。然而，我们的模拟表明，这是可能会改变，由于钉扎层各向异性的损失时，减少设备的尺寸。
英文摘要：
The effect of undesirable high-frequency free-layer switching in magnetic multilayer systems, referred to as back hopping, is investigated by means of the spin-diffusion model. A possible origin of the back-hopping effect is found to be the destabilization of the pinned layer which leads to perpetual switching of both layers. The influence of different material parameters on the critical switching currents for the free and pinned layer is obtained by micromagnetic simulations. It is found that the choice of a free-layer material with low polarization $β$ and saturation magnetization $M_s$, and a pinned-layer material with high $β$ and $M_s$ leads to a low free-layer critical current and a high pinned-layer critical current and hence reduces the likelihood of back hopping. While back hopping was observed in various types of devices, there are only few experiments that exhibit this effect in perpendicularly magnetized systems. However, our simulations suggest, that this is likely to change due to loss of pinned-layer anisotropy when decreasing device sizes.
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