Patent ID: 8123832

Claim:
An R-T-B system sintered magnet comprising a sintered body comprising, as a main phase of the sintered body, grains mainly comprising an R 2 T 14 B compound and comprising at least one of Dy and Tb as a heavy rare earth element and at least one of Nd and Pr as a light rare earth element, the R-T-B system sintered magnet being characterized in that: the sintered body has a composition comprising R: 25 to 37 wt %, B: 0.5 to 2.0 wt %, Co: 3.0 wt % or less, Al: 0.03 to 0.30 wt %, Cu: 0.01 to 0.15 wt %, and the balance: Fe and inevitable impurities, wherein R represents the heavy rare earth elements in an amount of 0.1 to 10 wt %; the sintered body comprises the grains each having a core-shell structure consisting of a single inner shell part and a single outer shell part surrounding the inner shell part; the concentration of the heavy rare earth element in the inner shell part is 20 to 95% of the concentration of the heavy rare earth element in the periphery of the outer shell part; in the grains each comprising the inner shell part and the outer shell part, (L/r) ave falls within a range from 0.10 to 0.25; and in a section thereof, the proportion of the number of the grains each having the core-shell structure to the total number of the grains forming the sintered body is 20% or more; wherein: R represents one or more rare earth elements inclusive of Y; T represents one or more transition metal elements wherein Fe or Fe and Co are essential; L represents the shortest distance from the periphery of the grain to the inner shell part; r represents the equivalent diameter of the grain; and (L/r) ave represents the average value of L/r for the grains, present in the sintered body, having the core-shell structure.