Strain-mediated spin-orbit torque switching for magnetic memory.

Spin-orbit torque (SOT) represents an energy efficient method to control magnetization in magnetic memory devices. However, deterministically switching perpendicular memory bits usually requires the application of an additional bias field for breaking lateral symmetry. Here we present a new approach of field-free deterministic perpendicular switching using a strain-mediated SOT switching method. The strain-induced magnetoelastic anisotropy breaks the lateral symmetry, and the resulting symmetry-breaking is controllable. A finite element model and a macrospin model are used to numerically simulate the strain-mediated SOT switching mechanism. The results show that a relatively small voltage (${\pm}0.5$ V) along with a modest current ($3.5 \times 10^{7} A/cm^{2}$) can produce a 180{\deg} perpendicular magnetization reversal. The switching direction (up or down) is dictated by the voltage polarity (positive or negative) applied to the piezoelectric layer in the magnetoelastic/heavy metal/piezoelectric heterostructure. The switching speed can be as fast as 10 GHz. More importantly, this control mechanism can be potentially implemented in a magnetic random-access memory system with small footprint, high endurance and high tunnel magnetoresistance (TMR) readout ratio.