HYSTERESIS LOOPS AT DIFFERENT TEMPERATURES FOR MELT-SPUN ND13FE77B10

Hysteresis loops of melt-spun Nd13Fe77B10 were measured at different t emperatures between 4.2 K and 250 K. The loops were analysed on the ba sis of the micromagnetism using the finite element technique. By fitti ng the calculated H-i(c), with the experiment, the value of the exchan ge constant across the inter-grain boundary was estimated to be about 90% of that across the inner-grain boundary, H-i(c), increases to a ma ximum at the spin reorientation temperature T-s and then decreases wit h increasing temperature. With decrease of the exchange interaction ac ross the grain boundary, H-i(c), decreases below T-s, and increases ab ove T-s, and the Stoner-Wohlfarth model provides the theoretical lower and upper limits of H-i(c), below and above T-s, respectively. The ca lculations reproduce the hysteresis loops fairly well. The magnetizati on proceeds by noncoherent rotation, and the spin distribution becomes quite non-uniform in some grains when H decreases to near H-i(c).