Small-amplitude magnetization dynamics in permalloy elements investigated by time-resolved wide-field Kerr microscopy

Abstract

A wide-field polarization microscope, optimized for Kerr microscopy was extended with a mode-locked pulsed laser illumination source to investigate time-dependent magnetization processes with picosecond resolution, thus providing the possibility to directly compare the quasistatic with the dynamic magnetization response. Square-shaped ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ elements were excited by fast magnetic field pulses aligned along and diagonally to the elements, respectively. Starting from the Landau ground state, the magnetic response to the excitation is dominated by a fast rotation of magnetization followed by slow relaxation, mostly through domain wall motion, back into the Landau state. Spike domains in the corners of the element form during the fast rotational process. Low angle domains with oscillatory behavior develop in the low dynamic permeability closure domains. Slow motion of the center vortex over several nanoseconds is recorded. The direct comparison of the dynamic and the static domain patterns is necessary for a understanding of all details of the magnetization processes.