Spin-orbit torque induced magnetisation dynamics and switching in CoFeB/Ta/CoFeB system with mixed magnetic anisotropy

TL;DR

This study investigates how spin-orbit torque induces magnetisation switching in a CoFeB/Ta/CoFeB trilayer with mixed magnetic anisotropies, revealing the influence of Ta spacer thickness on magnetic coupling and switching behavior.

Contribution

It demonstrates field-free SOT-induced switching in a CoFeB/Ta/CoFeB system with tunable magnetic coupling via Ta thickness variation.

Findings

Critical SOT current density increases as Ta thickness decreases.

Field-free switching occurs within a specific Ta thickness range with ferromagnetic IEC.

Interlayer exchange coupling affects magnetic anisotropy orientation and switching dynamics.

Abstract

Spin-orbit torque (SOT) induced magnetisation switching in CoFeB/Ta/CoFeB trilayer with two CoFeB layers exhibiting in-plane magnetic anisotropy (IPMA) and perpendicular magnetic anisotropy (PMA) is investigated. Interlayer exchange coupling (IEC), measured using ferromagnetic resonance technique is modified by varying thickness of Ta spacer. The evolution of the IEC leads to different orientation of the magnetic anisotropy axes of two CoFeB layers: for thicker Ta layer where magnetisation prefers antiferromagnetic ordering and for thinner Ta layer where ferromagnetic coupling exists. Magnetisation state of the CoFeB layer exhibiting PMA is controlled by the spin-polarized current originating from SOT in $\mu m$ sized Hall bars. The evolution of the critical SOT current density with Ta thickness is presented, showing an increase with decreasing $t_\mathrm{Ta}$, which coincides with the coercive field dependence. In a narrow range of $t_\mathrm{Ta}$ corresponding to the ferromagnetic IEC, the field-free SOT-induced switching is achieved.