A Specific Temperature Corresponding to Domain Structure Formation in Saturable Multi-domain Grains in Dy-free Nd_2Fe_(14)B Sintered Magnets

摘要

The Curie temperature (T_c) and the Neel temperature (T_N) are well known specific temperatures in hard magnetic materials. The T_c in Nd_2Fe_(14)B sintered magnets were measured by Hirosawa et al. and determined to be about 583K. Concerning to the T_c, the temperature dependence of magnetic anisotropy constants such as K_1 and K_2 factors were also studied by Cadogan et al.. Another specific temperature corresponding to domain structure re-formation in magnetized single-domain grains that are originally multi-domain state in thermally demagnetized state was never reported in previous studies. The authors found this kind of specific temperature in Nd_2Fe_(14)B sintered magnets. In this study, we will report the details of measurements and of the specific temperature. Experimentals and Results The samples in this study are Dy-free Nd_2Fe_(14)B sintered magnets of NEOMAX-50 type of the specification in NEOMAX Co., Ltd., Japan. The samples contain 0.1-0.2wt. percent of Al and Cu as additives. The sample shape is 5mm X 5mm X 6mm of nearly cubic and the surface effects on magnetization curves are almost negligible. The alignment of crystal grains is very well and the dispersion angle determined from the remanences in parallel and in perpendicular directions to the grain orientated direction is about 1.6~0.