PROCESS FOR PRODUCING RARE-EARTH MAGNET, AND RARE-EARTH MAGNET

摘要

A process for producing a rare-earth magnet represented by neodymium magnet (Nd2Fe14B) is provided, in which use is made of a heat treatment method that can heighten the magnetic properties, in particular, coercive force. Also provided is a novel rare-earth magnet of a nanocrystalline structure. The process for producing a rare-earth magnet comprises: a step in which a melt having a rare-earth magnet composition is rapidly cooled to form rapidly cooled thin pieces having a nanocrystalline structure; a step in which the rapidly cooled thin pieces are sintered; a step in which the resultant sintered object is subjected to an orientation treatment; and a step in which the sintered object is subjected to a heat treatment at a temperature which is high enough to enable the grain boundary phase to diffuse or move and which is low enough to prevent the crystal grains from enlarging. Desirably, an element that lowers the temperature at which the grain boundary phase becomes capable of diffusing or moving has been added to the rare-earth magnet composition. The rare-earth magnet of a nanocrystalline structure satisfies the following (i) to (iii): (i) the degree of crystallinity (I(410)/Ibase) is 8.0 or more, (ii) the degree of orientation (Mr/Ms) is 0.7-1.0, and (iii) the grains have an aspect ratio [(major-axis length):(minor-axis length)] of from 1:1 to 10:1.