In spin-transfer torque magnetoresistive random access memory, the magnetization dynamics of a free layer is usually assumed to be determined by the torque created via a position-independent current density. In circuits, however, it is the voltage, not the current density, which stays fixed during switching. Therefore, the approximate evaluation of the torque based on a fixed current density becomes questionable in modern magnetic tunnel junctions with a tunneling magnetoresistance ratio of about 200%, where the current density across the structure can vary by a factor of three. In this work, we compare the switching times obtained within a fixed voltage assumption with those from the approximate fixed current density assumption. We demonstrate that the assumption of a fixed current can reproduce the correct switching if the current is appropriately adjusted. It is shown that the correction to the current is not universal and depends on various factors such as TMR, temperature, the size of the structure and resistance area.

中文翻译：

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垂直STT-MRAM在固定电压和固定电流下的开关分析

在自旋转移力矩磁阻随机存取存储器中，通常假设自由层的磁化动力学由通过与位置无关的电流密度产生的力矩确定。然而，在电路中，在开关期间保持固定的是电压，而不是电流密度。因此，在隧道磁阻比约为 200% 的现代磁隧道结中，基于固定电流密度对扭矩的近似评估变得有问题，其中穿过结构的电流密度可以以三倍的系数变化。在这项工作中，我们将固定电压假设中获得的开关时间与近似固定电流密度假设中获得的开关时间进行比较。我们证明，如果电流适当调整，固定电流的假设可以重现正确的开关。结果表明，对电流的修正并不是通用的，它取决于各种因素，如TMR、温度、结构尺寸和电阻面积。