Method for manufacturing r-t-b based sintered magnet

A method for manufacturing an R-T-B based sintered magnet, which comprises:

• 1) a step of preparing an R-T-B based sintered magnet material by sintering a molded body, the R-T-B based sintered magnet material comprising:
• 27.5% or more by mass and 34.0% or less by mass of R
• (R being at least one element of rare earth elements and indispensably containing Nd);
• 0.85% or more by mass and 0.93% or less by mass of B;
• 0.20% or more by mass and 0.70% or less by mass of Ga;
• more than 0.2% by mass and 0.50% or less by mass of Cu;
• 0.05% or more by mass and 0.5% or less by mass of Al;
• and
• 0% or more by mass and 0.1% or less by mass of M
• (M being one or both of Nb and Zr), with the balance being T (T being Fe and Co, and 90% or more of T in terms of mass ratio being Fe) and inevitable impurities, the R-T-B based sintered magnet material satisfying inequality expressions (1) and (2) below:
• [T]−72.3[B]>0 (1)
• ([T]−72.3[B])/55.85<13[Ga]/69.72 (2)
• where [T] is a T content in percent by mass, [B] is a B content in percent by mass, and [Ga] is a Ga content in percent by mass;
• 2) a high-temperature heat treatment step of heating the R-T-B based sintered magnet material to a heating temperature of 730° C. or higher and 1,020° C. or lower and then cooling the R-T-B based sintered magnet material to 300° C. at a cooling rate of 5° C./min or more;
• and
• 3) a low-temperature heat treatment step of heating the R-T-B based sintered magnet material after the high-temperature heat treatment step to 440° C. or higher and 550° C. or lower.