Spin-Orbit Coupling of Conduction Electrons in Magnetization Switching

Strong magnetic field pulses associated with a relativistic electron bunch can imprint switching patterns in magnetic thin films that have uniaxial in-plane anisotropy. In experiments with Fe and FeCo alloy films the pattern shape reveals an additional torque acting on magnetization during the short (in the 100fs time scale) magnetic field pulse. The magnitude of the torque is as high as 15% of the torque from the magnetic field. The torque symmetry is that of a uniaxial anisotropy along the direction of the eddy current screening the magnetic field. Spin-orbit interaction acting on the conduction electrons can produce such a torque with the required symmetry and magnitude. The same interaction causes the anomalous Hall current to be spin-polarized, exerting a back reaction on magnetization direction. Such a mechanism may be at work in all-optical laser switching of magnetic materials.