RELATION BETWEEN THE MAGNETIC-PROPERTIES OF ND16FE76B8 MAGNETS AND HOMOGENEITY OF THE ND2FE14B PHASE

The homogeneity range of the Nd2Fe14B phase was investigated. It was f ound that magnets which were annealed at about 500 degrees C and quick ly cooled exhibited some solution of Nd dissolved in the lattice of th e Nd2Fe14B phase. This was indicated in the changes of the tetragonali ty of the unit cell, microhardness and magnetic properties. The increa sed coercivity of magnets annealed at 500 degrees C is considered to b e attributed to the formation of the Guinier-Preston I-like zones of N d atoms in the structure of the Nd2Fe14B phase which introduces a doma in wall pinning contribution to the coercivity mechanism. The effect o f thermocycling at temperatures close to the Curie temperature of the Nd2Fe14B phase was also investigated. As a result of the alternating c ompressive and tensile stresses during cycling, changes in the mean gr ain size, phase constitution and magnetic properties were observed. (C ) 1998 Elsevier Science B.V.