All-optical probe of magnetization precession modulated by spin–orbit torque

Laser-induced magnetization precession modulated by an in-plane direct current was investigated in a W/CoFeB/MgO micron-sized strip using an all-optical time-resolved magneto-optical Kerr effect microscope. We observed a relatively large change in the precession frequency, owing to a current-induced spin–orbit torque. The generation efficiency of the spin–orbit torque was evaluated as −0.35 ± 0.03, which was in accordance with that evaluated from the modulation of damping. This technique may become an alternate method for the evaluation of spin–orbit torque.