Magnetic domains in sintered Fe-Nd-B magnets

Abstract

Magnetic domain structures in sintered Fe‐Nd‐B magnets from several suppliers were studied using the polar Kerr effect. Most grains were multidomain in the thermally demagnetized state. Measurement of average surface domain width in several large grains yielded a domain‐wall energy of 25 ergs/cm² for the Fe₁₄Nd₂B primary phase. After saturation and subsequent demagnetization in reverse field, most grains were again multidomain. Consistent with this observation, thermal remagnetization was small. A Fe‐Nd‐B‐based magnet with much higher coercivity showed a much higher percentage of single‐domain grains in the field‐demagnetized state and a much higher thermal remagnetization, i.e., a behavior more nearly similar to earlier results on sintered Co₅Sm magnets.