Patent ID: 7488394

Claim:
A rare earth permanent magnet in the form of a sintered magnet body having an alloy composition R 1 a R 2 b T c A d F e O f M g wherein R 1 is at least one element selected from rare earth elements inclusive of Sc and Y and exclusive of Tb and Dy, R 2 is one or both of Tb and Dy, T is one or both of iron and cobalt, A is one or both of boron and carbon, F is fluorine, O is oxygen, and M is at least one element selected from the group consisting of Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, and W, a through g indicative of atom percents of the corresponding elements in the alloy have values in the range: 10≦a+b≦15, 3≦d≦15, 0.01≦e≦4, 0.04≦f≦4, 0.01≦g≦11, the balance being c, said magnet body having a center and a surface, wherein constituent elements F and R 2 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 R 2 /(R 1 +R 2 ) which is on the average higher than the concentration of R 2 /(R 1 +R 2 ) contained in primary phase grains of (R 1 ,R 2 ) 2 T 14 A tetragonal system form a three-dimensional network structure which is continuous from the magnet body surface to a depth of at least 10 μm.