Critical current destabilizing perpendicular magnetization by the spin Hall effect

TL;DR

This paper investigates how the spin Hall effect influences the critical current required to destabilize perpendicular magnetization, revealing conditions under which this current can be significantly reduced for efficient magnetic switching.

Contribution

It introduces a comprehensive model including dampinglike and fieldlike torques, showing how the fieldlike torque can lower the critical current depending on its sign and system parameters.

Findings

Critical current is independent of damping without fieldlike torque.

Properly signed fieldlike torque can significantly reduce the critical current.

Analytical and numerical results confirm the current scaling with damping constant.

Abstract

The critical current needed to destabilize the magnetization of a perpendicular ferromagnet via the spin Hall effect is studied. Both the dampinglike and fieldlike torques associated with the spin current generated by the spin Hall effect is included in the Landau-Lifshitz-Gilbert equation to model the system. In the absence of the fieldlike torque, the critical current is independent of the damping constant and is much larger than that of conventional spin torque switching of collinear magnetic systems, as in magnetic tunnel junctions. With the fieldlike torque included, we find that the critical current scales with the damping constant as $\alpha^{0}$ (i.e., damping independent),$\alpha$, and $\alpha^{1/2}$ depending on the sign of the fieldlike torque and other parameters such as the external field. Numerical and analytical results show that the critical current can be significantly reduced when the fieldlike torque possesses the appropriate sign, i.e. when the effective field associated with the fieldlike torque is pointing opposite to the spin direction of the incoming electrons. These results provide a pathway to reducing the current needed to switch magnetization using the spin Hall effect.