Switching of perpendicular magnetization by spin-orbit torques in the absence of external magnetic fields

摘要

Magnetization switching by current-induced spin-orbit torques (SOTs) is ofgreat interest due to its potential applications for ultralow-power memory andlogic devices. In order to be of technological interest, SOT effects need toswitch ferromagnets with a perpendicular (out-of-plane) magnetization.Currently, however, this typically requires the presence of an in-planeexternal magnetic field, which is a major obstacle for practical applications.Here we report for the first time on SOT-induced switching of out-of-planemagnetized Ta/Co20Fe60B20/TaOx structures without the need for any externalmagnetic fields, driven by in-plane currents. This is achieved by introducing alateral structural asymmetry into our devices during fabrication. The resultsshow that a new field-like SOT is induced by in-plane currents in suchasymmetric structures. The direction of the current-induced effective fieldcorresponding to this new field-like SOT is out-of-plane, which facilitatesswitching of perpendicular magnets. This work thus provides a pathway towardsbias-field-free SOT devices.