Rare earth permanent magnet and its preparation

A method for preparing a rare earth permanent magnet, comprising the steps of:

• disposing an alloy powder having an average particle size of up to 500 μm on a surface of a sintered body of the composition Ra-T1b-Bc wherein R is at least one element selected from rare earth elements inclusive of Y and Sc, T1 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≦c≦7.0, and the balance of b, said alloy powder having the composition R1i-M1j wherein R1 is at least one element selected from rare earth elements inclusive of Y and Sc, M1 is at least one element selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, “i” and “j” indicative of atomic percent are in the range:
• 15<j≦99 and the balance of i, and containing at least 70% by volume of an intermetallic compound phase, and
• heat treating the sintered body having the powder disposed on its surface at a temperature equal to or below the sintering temperature of the sintered body in vacuum or in an inert gas, for causing at least one element of R1and M1 in the powder to diffuse to grain boundaries in the interior of the sintered body and/or near grain boundaries within sintered body primary phase grains,
• said disposing step including grinding an alloy having the composition and R1i-M1j and containing at least 70% by volume of an intermetallic compound phase into a powder having an average particle size of up to 500 μm, dispersing the powder in an organic solvent or water, applying the resulting slurry to the surface of the sintered body, and drying.