Abstract
A full numerical analysis, which takes into account the effects of the spin Hall effect, interfacial Dzyaloshinskii–Moriya interaction, and thermal fluctuations, is carried out in in-plane magnetized CoFeB/MgO/CoFeB/high-resistivity tungsten (β-W) nanoelements. The analysis is focused on the investigation of the underlying mechanisms of magnetic-field-free spin–orbit torque (SOT)-driven magnetization reversal process on subnanosecond time scales. It is found that the magnetization in the free magnetic layer can be electrically toggled between the parallel and antiparallel alignment with respect to the fixed magnetic layer without the assistance of an external magnetic field, in which the out-of-plane canting of the magnetic moments at the element edges plays a significant role in the nucleation and subsequent expansion of the reversed magnetization. Furthermore, the thermally activated magnetization process combined with the SOT effect is found to significantly reduce the effective energy barrier to the magnetization reversal and alter the details of the SOT-driven magnetization process in nanomagnets.
Highlights
We report detailed micromagnetic studies of magnetic-field-free spin–orbit torque (SOT)-induced magnetization switching dynamics on nanosecond time scales in nanoelements consisting of CoFeB/MgO/CoFeB multilayers
It is found that the out-of-plane canting of the magnetic moments at the element edges plays a significant role in the SOT-driven magnetization dynamics
An input charge current on the order of a few 100 μA passes through the W current line, and the charge current is converted to a transverse spin current via the spin Hall effect
Summary
We report detailed micromagnetic studies of magnetic-field-free SOT-induced magnetization switching dynamics on nanosecond time scales in nanoelements consisting of CoFeB/MgO/CoFeB multilayers. It should be noted that the thermally activated process can be strongly dependent on the charge current, which significantly modifies the effective energy barrier to the magnetization reversal.19,21 The result shown in Fig. 2(a) indicates that the SOT effect combined with thermal fluctuations can effectively alter the details of the SOT-driven magnetization process in nanomagnets.19 This finding suggests that the micromagnetic modeling without taking the thermal effects into account may severely mislead in the understanding of the underlying mechanisms, leading to the SOT-mediated magnetization switching.
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