Shape Anisotropy Enabled Field Free Switching of Perpendicular Nanomagnets

Abstract: Spin Orbit Torque-Magnetic Random Access Memory (SOT-MRAM) is being developed as a successor to the Spin transfer torque MRAM (STT-MRAM) owing to its superior performance on the metrics of reliability and read-write speed. SOT switching of perpendicularly magnetized ferromagnet in the heavy metal/ferromagnet bilayer of SOT-MRAM unit cell requires an additional external magnetic field to support the spin-orbit torque generated by heavy metal to cause deterministic switching. This complexity can be overcome if an internal field can be generated to break the switching symmetry. We experimentally demonstrate that by engineering the shape of ferromagnet, an internal magnetic field capable of breaking the switching symmetry can be generated, which allows for deterministic switching by spin-orbit torques. We fabricated nanomagnets of Cobalt with triangular shape on top of Platinum and showed external magnetic field free switching between the two stable states of magnetization by application of nano-second voltage pulses. The experimental findings are consistent with the micro-magnetic simulation results of the proposed geometry.