Patent ID: 8277578

Claim:
A rare earth permanent magnet, which is prepared by disposing an alloy powder on a surface of an original sintered body of the composition R a -T 1 b -B c wherein R is at least one element selected from rare earth elements inclusive of Y and Sc, T 1 is at least one element selected from Fe and Co, B is boron, “a,” “b” and “c” indicative of atomic percent are in the range: 12≦a≦20, 4.0≦c7.0, and the balance of b, said alloy powder having the composition M 1 d - M 2 e wherein each of M 1 and M 2 is at least one element selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, M 1 is different from M 2 , “d” and “e” indicative of atomic percent are in the range: 0.1≦e≦99.9 and the balance of d, and containing at least 70% by volume of an intermetallic compound phase, and heat treating the sintered body having the alloy powder disposed on its surface at a temperature equal to or below the sintering temperature of the original sintered body in vacuum or in an inert gas, wherein at least one element of M 1 and at least one element of M 2 in the alloy powder is diffused to grain boundaries in the interior of the sintered body and/or near grain boundaries within sintered body primary phase grains, and not into the interior of primary phase grains, so that the coercive force of the magnet is increased over the magnet properties of the original sintered body.