Method for producing sintered R—T—B based magnet and diffusion source

1. 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.

2. The method for producing a sintered R-T-B based magnet of claim 1 , wherein the sintered R-T-B based magnet work satisfies the following inequality (1):

[ T ]/55.85>14[ B ]/10.8  (1)

(where [T] is the T content in mass %, and [B] is the B content in mass).

3. The method for producing a sintered R-T-B based magnet of claim 1 , wherein a Ga amount in the sintered R-T-B based magnet work is 0 to 0.5 mass %.

4. The method for producing a sintered R-T-B based magnet of claim 1 , wherein an Nd content in the Pr—Ga alloy is equal to or less than an inevitable impurity content.