Observation of frequency dependent resonances in magnetic vortex core gyration using time-resolved magneto-optical Kerr microscope with pulsed semiconductor laser illumination

Frequency dependent resonance of magnetic vortex core gyration in micrometer sized permalloy squares was observed by time-resolved magneto-optical Kerr microscope using pulsed semiconductor lasers as a light source in the stroboscopic method. Uniform and efficient laser illumination was realized by a speckle reducer consisting of an oscillating multimode optical fiber and a microbending mode scrambler. The resonance frequency of the same sized permalloy squares showed a non-uniformity of up to 15%, suggesting the flatness of the underlayer has a strong influence on the gyration motion.