Patent ID: 7988795

Claim:
An R-T-B-C rare earth sintered magnet wherein R is at least one rare earth element selected from the group consisting of Ce, Pr, Nd, Tb, and Dy, T is iron or a mixture of iron and at least one other transition metal, B is boron, and C is carbon, which magnet is obtained by: mixing (II) 1 to 20% by weight of an R-rich R-T-B—C sintering aid alloy consisting essentially of 50 wt %≦R≦65 wt %, 0.3 wt %≦B≦0.9 wt %, 0.01 wt %≦C≦0.5 wt %, 0.1 wt %≦Al≦1.0 wt %. 0.1 wt %≦Cu≦5.0 wt %, and the balance of T, (III) 10 to 50% by weight of an R—O 1−x —F 1+2x and/or R—F y powder having an average particle size of 0.5 to 50μm wherein x is an arbitrary real number of 0 to 1 and y is 2 or 3, and (I) the remainder of a R-T-B—C primary phase magnet matrix alloy powder consisting essentially of 25 wt %≦R≦35 wt %, 0.8 wt %≦B≦1.4 wt %, 0.01 wt %≦C≦0.5 wt %, 0.1 wt %≦Al≦1.0 wt %, and the balance of T, pulverizing the mixture through a jet mill in a nitrogen stream to an average particle size of 0.01 to 30 μm, compacting the mixture in a magnetic field into a compact, sintering and heat treating the compact, wherein the rare earth sintered magnet has a sintered structure consisting of an R 2 T 14 B structure crystal primary phase and a grain boundary phase, said grain boundary phase consisting essentially of 40 to 98% by volume (a volume fraction in the grain boundary phase) of R-O 1−x -F 1+2x and/or R-F y wherein x is an arbitrary real number of 0 to 1 and y is 2 or 3, 1 to 50% by volume of a compound phase selected from R-O, R-O-C, and R-C compounds, and mixtures thereof, 0.05 to 10% by volume of a R-T phase, 0.05 to 20% by volume of a B-rich phase (R 1+ε Fe 4 B 4 ) or M-B 2 phase wherein M is at least one element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W, and the balance of an R-rich phase.