Analysis of the Demagnetization Process of Nd-Fe-B Sintered Magnets at Elevated Temperatures by Magnetic Domain Observation Using a Kerr Microscope

摘要

Magnetization reversal and its propagation in sintered Nd–Fe–B magnets were clearly observed at elevated temperatures up to 150 °C using a Kerr microscope, image processing, and photo editing. Simultaneous magnetization reversal in several grains along the easy axis direction occurred at elevated temperature, and the extent of simultaneous magnetization reversal increased with temperature. This indicates that reduction in the coercivity of Nd–Fe–B sintered magnets at elevated temperatures is attributable to decrease in anisotropy and insufficient pinning of domain walls at grain boundaries.