Reduced Spin-Orbit Torque Switching Current by Voltage-Controlled Easy-Cone States

Abstract

Spin-orbit torque (SOT) promises fast and reliable switching of the perpendicular magnetization in spintronic devices, such as magnetic random-access memory or spin logic devices. To apply the SOT technology to practical devices with low power consumption, it is necessary to reduce the switching current. To this end, most of the research to date in this area has focused on improving the charge-to-spin conversion efficiency in heavy metal/ferromagnet structures. In this study, it is reported that the SOT switching current is significantly reduced by modulating magnetic easy-cone states through voltage-controlled magnetic anisotropy (VCMA). The introduction of a thin Pt layer at the CoFeB/MgO interface enhances the VCMA effect, allowing a magnetic easy-cone state of CoFeB to be formed and controlled by the gate voltage. As a result, the SOT switching current density is reduced by up to 50% when the easy-cone angle is changed from 0 degrees to 58 degrees. Furthermore, the magnetic easy-cone state is gradually modulated in a reversible and non-volatile manner, facilitating multilevel spintronic devices.