R—Fe—B sintered magnet and making method

An R—Fe—B base sintered magnet of a composition consisting essentially of:

• 12 to 17 at % of R which comprises at least Nd and Pr, and optionally one or more elements selected from a group consisting of yttrium and rare earth elements other than Nd and Pr,
• 0.1 to 3 at % of M1 which is at least one element selected from the group consisting of Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi,
• 0.05 to 0.5 at % of M2 which is at least one element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W,
• 4.8+2×m to 5.9+2×m at % of B wherein m stands for atomic concentration of M2,
• up to 10 at % of Co,
• up to 0.5 at % of carbon,
• up to 1.5 at % of oxygen,
• up to 0.5 at % of nitrogen, and
• the balance of Fe,
• the R—Fe—B base sintered magnet containing R2(Fe,(Co))14B intermetallic compound as a main phase, and having a coercivity of at least 10 kOe at room temperature, wherein
• the magnet contains a M2 boride phases at grain boundary triple junctions, but not including R1.1Fe4B4 compound phase, has a core/shell structure that the main phase is covered with grain boundary phases comprising an amorphous and/or sub-10 nm nanocrystalline R—Fe(Co)-M1 phase consisting essentially of 25 to 35 at % of R, 2 to 8 at % of M1, up to 8 at % of Co, and the balance of Fe, or the R—Fe(Co)-M1 phase and a crystalline or a sub-10 nm nano-crystalline and amorphous R-M1 phase having at least 50 at % of R, wherein a surface area coverage of the R—Fe(Co)-M1 phase on the main phase is at least 50%, and the width of the intergranular grain boundary phase is at least 10 nm and at least 50 nm on the average.