Analysis of Hysteresis loops at different temperatures for melt-spun Nd₁₃Fe₇₇B₁₀

Abstract

Hysteresis loops of melt-spun Nd₁₃Fe₇₇B₁₀ were measured in the temperature range between 4.2 K and 250 K. With increase of temperature, _iH_c increases to a maximum at the spin reorientation temperature T_s and then decreases. The loops and the spin distributions were calculated by the micromagnetic finite element method. The exchange interaction across the grain boundary was estimated to be about 90 % of that within a grain. The calculations reproduce the experiment well. The weaker the exchange interaction across the grain boundary, the smaller the _iH_c below T_s and the larger the _iH_c above T_s, and so the Stoner-Wohlfarth model provides the theoretical lower and upper limits of _iH_c below and above T_s, respectively. The magnetization proceeds by the non-coherent rotation and the spin distribution becomes quite nonuniform when the field decreases to around -_iH_c.