Picosecond wide-field magneto-optical imaging of magnetization dynamics of amorphous film elements

Abstract

Time-resolved wide-field magneto-optical microscopy with picosecond time resolution and with phase-locked harmonic excitation is used to image the fundamental dynamic modes of magnetic domain and domain-wall states in soft-magnetic thick film elements. By analyzing mirrored domain states, the pure in-plane and out-of-plane dynamic magnetic response under a continuous microwave excitation is extracted simultaneously. Domain-wall oscillations and local domain response, including transversely aligned and closure domain states, are visualized below, at, and above the resonance frequency of the magnetic elements. Regions of different high-frequency permeability are distinguished from the laterally resolved measurements. Despite nearly constant precessional frequency, a strong mode amplitude variation is found with varying the magnetic bias field, which is correlated to the exhibited change of the individual domain structure. Inhomogeneous out-of-phase precessional modes within the individual domains occur close to a state of domain instability. The imaging results are compared to existing models of flux response. Magnetic domain knowledge and precise dynamic imaging is needed for the understanding of the dynamic magnetization behavior of even basic domain structures beyond the magnetic material's elementary properties.