Unveiling Temperature-Dependence Mechanisms of Perpendicular Magnetic Anisotropy at Fe/MgO Interfaces
Unveiling Temperature-Dependence Mechanisms of Perpendicular Magnetic Anisotropy at Fe/MgO Interfaces
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DOI：
10.1103/physrevapplied.17.054041
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发表时间：
2022-05-25
影响因子：
4.6
通讯作者：
Chshiev, Mairbek
中科院分区：
文献类型：
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作者：
Ibrahim, Fatima;Hallal, Ali;Chshiev, Mairbek
在磁性过渡金属氧化物界面处的垂直磁各向异性是构建用于自旋转移矩磁性随机存取存储器（STT MRAM）的面外磁化磁性隧道结的关键要素。尺寸缩小使得磁性对热效应更敏感。因此，理解磁各向异性的温度依赖性变得至关重要。在这项工作中，我们从理论上解决了典型的Fe/MgO基结构的磁各向异性和磁化强度的温度依赖性之间的相关性。特别是，背后的实验报告的偏差Callen和Callen缩放幂律的可能机制进行了分析。在理想界面处，第一性原理计算揭示了（i）与一阶相比小的高阶各向异性常数和（ii）增强的交换常数。考虑到这两个内在的原子模拟的影响，总的和层分辨各向异性的温度依赖性被发现遵循Callen和Callen标度幂律，从而排除了内在的微观机制偏离这一法律。此外，揭示了两种可能的外在宏观机制，即死层的影响，通常存在于存储层的STT-MRAM单元和界面磁各向异性的空间不均匀性。关于第一种机制，我们表明，死层的存在往往会降低标度指数。在第二种机制中，增加界面垂直磁各向异性中的不均匀性的百分比被揭示为降低标度指数。这些结果使我们能够连贯地解释与各向异性和磁化热变化相关的标度指数在早期实验中的差异。这对于理解STT-MRAM应用中存储层磁化的热稳定性是至关重要的。
The perpendicular magnetic anisotropy at magnetic transition-metal-oxide interfaces is a key element in building out-of-plane magnetized magnetic tunnel junctions for spin-transfer-torque magnetic random access memory (STT MRAM). Size downscaling renders magnetic properties more sensitive to thermal effects. Thus, understanding the temperature dependence of the magnetic anisotropy becomes crucial. In this work, we theoretically address the correlation between the temperature dependence of magnetic anisotropy and magnetization in typical Fe/MgO-based structures. In particular, the possible mechanisms behind the experimentally reported deviations from the Callen and Callen scaling power law are analyzed. At ideal interfaces, first-principles calculations reveal (i) small high-order anisotropy constants compared to first order and (ii) enhanced exchange constants. Considering these two intrinsic effects in the atomistic simulations, the temperature-dependence of the total and layer-resolved anisotropy are found to follow the Callen and Callen scaling power law, thus ruling out an intrinsic microscopic mechanism underlying deviations from this law. Besides, two possible extrinsic macroscopic mechanisms are unveiled, namely the influence of the dead layer, often present in the storage layer of STT-MRAM cells and the spatial inhomogeneities of the interfacial magnetic anisotropy. About the first mechanism, we show that the presence of a dead layer tends to reduce the scaling exponents. In the second mechanism, increasing the percentage of inhomogeneity in the interfacial perpendicular magnetic anisotropy is revealed to decrease the scaling exponent. These results allow us to coherently explain the difference in scaling exponents relating anisotropy and magnetization thermal variations reported in earlier experiments. This is crucial for the understanding of the thermal stability of the storage-layer magnetization in STT-MRAM applications.