US Patent 7488394 Rare earth permanent magnet

A rare earth permanent magnet is in the form of a sintered magnet body having a composition R1aR2bTcAdFeOfMg wherein F and R2 are distributed such that their concentration increases on the average from the center toward the surface of the magnet body, and grain boundaries having a concentration of R2/(R1+R2) which is on the average higher than the concentration of R2/(R1+R2) contained in primary phase grains of (R1,R2)2T14A tetragonal system form a three-dimensional network structure which is continuous from the magnet body surface to a depth of at least 10 μm. The invention provides R—Fe—B sintered magnets which exhibit a high coercive force.