Femtosecond pump-probe MOKE microscopy for an ultrafast spin dynamics study

Abstract

We report a femtosecond pump-probe magneto-optical Kerr effect (MOKE) microscopic system enabling the study of vectorial spin dynamics with submicron spatial resolution using an 11-fs pulsed laser source. We applied the system to investigate the spin precessional motion of a patterned disk (2.8 mu m x 3.0 mu m x 50 nm) of permalloy placed in an in-plane biasing magnetic-field. The vector components of the spins perpendicular to the field's direction showed a phase difference of about pi/2, which represents an elliptic motion in the magnetic phase trajectory. A numerical calculation utilizing the Stoner model of the Landau-Lifshitz-Gilbert equation yielded a damping parameter of alpha = 0.016. A theoretical simulation with the shape of the magnetic field pulse, considering surface recombination of the photoconductive switch and multiple reflections of the waveguide, accurately predict the experimental observation of vectorial precessional motion.