The Role of Damping in Ultrafast Magnetization Reversal

Abstract

Ultrashort magnetic field pulses generated in the final focus test beam facility at the Stanford Linear Accelerator have been used to study fundamental properties of magnetization reversal in thin films with in-plane and perpendicular easy magnetization directions. For perpendicular magnetized samples we observe ring domains with Kenmicroscopy, which are reminiscent of the field contour during exposure. Their radii represent switching fields in quantitative agreement with the coherent rotation model. In this case switching is caused by a simple rotation of the magnetization around the effective field while the external field pulse is present and thus damping mechanisms do not play a major role. For films with an uniaxial anisotropy in the plane of the film we observe that smaller fields are sufficient to reverse the magnetization, provided that the field is orthogonal to the magnetization. In this geometry maximum torque is exerted on the spins. Precession of the magnetization around the demagnetizing field completes the reversal after the external field ceases to exist. In this case the remagnetization process takes considerably longer time, so that the effect of damping can no longer be neglected.