R-t-b rare earth sintered magnet having improved squareness ratio and method for producing same

Abstract

An R—T—B rare earth sintered magnet containing an R T B-type intermetallic compound as a main phase and thus having improved squareness ratio is produced by carrying out a reduction and diffusion method comprising the steps of (a) mixing oxide powder of at least one rare earth element R, T-containing powder, wherein T is Fe or Fe and Co, B-containing powder, and a reducing agent such as Ca, (b) heating the resultant mixture at 900-1350° C. in a non-oxidizing atmosphere, (c) removing reaction by-products from the resultant reaction product by washing, and (d) carrying out a heat treatment for Ca removal by heating the resultant R—T—B rare earth alloy powder at 900-1200° C. in vacuum at 1 Torr or less, followed by pulverization of the resultant alloy powder bulk, molding, sintering in vacuum, heat treatment, and surface treatment. The alloy powder bulk obtained by the heat treatment for Ca removal is preferably pulverized after removal of its surface layer.