Method for producing sintered r-t-b based magnet and diffusion source

A method for producing a sintered R-T-B based magnet, comprising:

• providing a sintered R-T-B based magnet work containing
• R:
• 27.5 to 35.0 mass % (where R is at least one rare-earth element, always including Nd),
• B:
• 0.80 to 0.99 mass %,
• Ga:
• 0 to 0.8 mass %,
• M:
• 0 to 2 mass % (where M is at least one of Cu, Al, Nb and Zr), and
• a balance T (where T is Fe, or Fe and Co) and inevitable impurities;
• providing a powder of a Pr—Ga alloy produced through atomization;
• subjecting the Pr—Ga alloy powder to a heat treatment at a temperature which is not lower than a temperature that is 250° C. below a melting point of the Pr—Ga alloy powder and which is not higher than the melting point, to obtain a diffusion source from the Pr—Ga alloy powder;
• and
• a diffusing step of placing the sintered R-T-B based magnet work and the diffusion source in a process chamber, and heating the sintered R-T-B based magnet work and the diffusion source to a temperature which is above 600° C. but not higher than 950° C., thereby allowing Pr and Ga contained in the diffusion source to diffuse from the surface into the interior of the sintered R-T-B based magnet work.