Domain behavior in sintered Nd-Fe-B magnets during field-induced and thermal magnetization change

Abstract

On sintered Nd-Fe-B permanent magnets, magnetic domain pattern changes in applied fields and at elevated temperatures were observed by the Kerr effect. Patterns on pole and side faces were recorded for different magnetization states in fields up to 17 kOe at 20 °C, and remanent patterns at temperatures up to TC. They are qualitatively interpreted. On pole faces, most grains are multidomain even at remanence. But the surface domains seen are not characteristic of the magnet interior. Side faces show mostly single-domain grains at remanence. These images appear to reflect bulk behavior. Walls are strongly pinned at grain boundaries but move easily in the main magnetic phase, a behavior analogous to that of sintered SmCo5.