Field-free ultrafast magnetization reversal of a nanodevice by a chirped current pulse via spin-orbit torque

Abstract

We investigate the magnetization reversal of a perpendicularly magnetized nanodevice using a chirped current pulse (CCP) via spin-orbit torques (SOTs). Our numerically simulated findings demonstrate that both the field-like (FL) and damping-like (DL) components of SOT in CCP can be efficiently utilized to induce ultrafast magnetization reversal without any symmetry-breaking means. For a wide frequency range of the CCP, the minimal current density is significantly smaller compared to the current density of conventional SOT-reversal. This ultrafast reversal is achieved due to the CCP triggering enhanced energy absorption (emission) of the magnetization from (to) the FL- and DL-components of SOT before (after) crossing over the energy barrier. We also verify the robustness of the CCP-driven magnetization reversal at room temperature. Moreover, this strategy is applicable also to induce field-free ultrafast and efficient switching of perpendicular synthetic antiferromagnetic and ferrimagnetic (SFi) nanodevices. The minimal current density of deterministic switching of the SFi system decreases significantly with the reduction of one layer's magnetization, mainly because the SOT amplitude is inversely proportional to the saturation magnetization. Therefore, this study enriches the basic understanding of field-free SOT-reversal and provides a way to realize ultrafast SOT-MRAM devices with various free layer designs.