Frequency-Induced Bulk Magnetic Domain-Wall Freezing Visualized by Neutron Dark-Field Imaging

We use neutron dark-field imaging to visualize and interpret the response of bulk magnetic domain walls to static and dynamic magnetic excitations in (110)-Goss textured iron silicon high-permeability steel alloy. We investigate the domain-wall motion under the influence of an external alternating sinusoidal magnetic field. In particular, we perform scans combining varying levels of dc_offset (0–30 A/m), oscillation amplitude A_ac (0–1500 A/m), and frequency f_ac (0–200 Hz). By increasing amplitude A_ac while maintaining constant values of dc_offset and f_ac, we record the transition from a frozen domain-wall structure to a mobile one. Vice versa, increasing f_ac while keeping A_ac and dc_offset constant led to the reverse transition from a mobile domain-wall structure into a frozen one. We show that varying both A_ac and f_ac shifts the position of the transition region. Furthermore, we demonstrate that higher frequencies require higher oscillation amplitudes to overcome the freezing phenomena. The fundamental determination and understanding of the frequency- induced freezing process in high-permeability steel alloys is of high interest to the further development of descriptive models for bulk macromagnetic phenomena. Likewise, the efficiency of transformers can be improved based on our results, since these alloys are used as transformer core material.