Abstract
Electrical and optical control of magnetization are of central importance in the research and applications of spintronics. Non-relativistic angular momentum transfer or relativistic spin-orbit coupling provide efficient means by which electrical current driven through a ferromagnet can exert a torque on the magnetization.
Ferromagnetic semiconductors like (Ga, Mn) As are suitable model systems with which to search for optical counterparts of these phenomena, where photocarriers excited by a laser pulse exert torque upon magnetization. Here, we report the observation of an optical spin-orbit torque (OSOT) in (Ga, Mn) As.
The phenomenon originates from spin-orbit coupling of non-equilibrium photocarriers excitated by helicity-independent pump laser pulses, which do not impart angular momentum. In our measurements of the time-dependent magnetization trajectories, the signatures of OSOT are clearly distinct from the competing thermal excitation mechanism, and OSOT can even dominate in (Ga, Mn) As materials with appropriately controlled micromagnetic parameters.