Magneto-optical analysis of domain-wall oscillations in garnet films

Abstract

Domain-wall oscillations have been analyzed in Bi-Ga and Bi-Gd-Pr-Ga substituted garnet films by magneto-optical effects at 6328 Å wavelength and under rf magnetic excitation of up to 50 MHz. The amplitude of wall oscillations in a stripe-domain structure was determined from the change of the light intensity transmitted by the garnet film placed between polarizer and analyzer. The detected signal is proportional to the variation θeff of the Faraday rotation associated with the wall displacement d as described by θeff =4dθs/P0, where θs and P0 are the specific Faraday rotation and the stripe period. The amplitudes of θeff and d are linear functions of the excitation magnetic field H at low frequencies, but present a saturation behavior at high frequencies. When subjected to the same excitation field amplitude, the two garnet series present different frequency dependencies of the wall displacement, which can be correlated with the magnetic susceptibility of the samples. After annealing at high temperatures, the oscillating amplitude d of wall displacement shows opposite evolutions for the two garnet series. These results are discussed using both a theoretical model of wall oscillation and the change of the basic magnetic properties of the garnet films after annealing.