Spin-orbit torque induced magnetization switching in nano-scale Ta/CoFeB/MgO

Abstract

We study the device size dependence of spin-orbit torque induced magnetization switching in a Ta/CoFeB/MgO structure with perpendicular easy axis. The miniaturization of the device from micrometer-sized wire to 80-nm dot results in the increase of the threshold current density J_th by one order, whereas J_th increases only slightly with further reducing the device size down to 30 nm. No significant increase in J_th is seen, as the current pulse width decreases from 100 ms down to 3 ns. We reveal that the switching in devices at reduced size is reasonably well explained by the macrospin model, in which the effects of both the Slonczewski-like torque and field-like torque are included.