R-Fe-B rare-earth sintered magnet and process for producing the same

1. A method for producing an R—Fe—B based rare-earth sintered magnet, the method comprising the steps of:

providing an R—Fe—B based rare-earth sintered magnet body including, as a main phase, crystal grains of an R 2 Fe 14 B type compound that includes a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R;

depositing an M layer, including a metallic element M that is at least one element selected from the group consisting of Al, Ga, In, Sn, Pb, Bi, Zn and Ag, on a surface of the R—Fe—B based rare-earth sintered magnet body;

depositing an RH layer, including a heavy rare-earth element RH that is at least one element selected from the group consisting of Dy, Ho and Tb, on the M layer; and

heating the R—Fe—B based rare-earth sintered magnet body, thereby diffusing the metallic element M and the heavy rare-earth element RH from the surface of the R—Fe—B based rare-earth sintered magnet body deeper inside the magnet.

2. The method of claim 1 , wherein the R—Fe—B based rare-earth sintered magnet body has a thickness of about 3 mm to about 10 mm.

3. The method of claim 2 , comprising the step of setting the weight of the RH layer yet to be diffused within the range of about 0.1% to about 1.0% of the weight of the R—Fe—B based rare-earth sintered magnet body.

4. The method of claim 1 , comprising the step of setting the temperature of the R—Fe—B based rare-earth sintered magnet body during diffusion within the range of about 300° C. to less than about 1,000° C.

5. The method of claim 1 , wherein the steps of depositing the M layer and the RH layer are carried out by a vacuum evaporation process, a sputtering process, an ion plating process, an ion vapor deposition process, an electrochemical vapor deposition process or a dipping process.