R-T-B based permanent magnet

An R-T-B based permanent magnet comprising an R-T-B sintered body and optionally a coating material thereon containing a heavy rare earth element not subjected to grain boundary diffusion heat treatment wherein,

• R is a rare earth element, T is an element other than the rare earth element, B, C, O or N, and B is boron,
• T at least includes Fe, Cu, Co and Ga,
• wherein in the R-T-B sintered body, a total of R content is 28.0 to 30.2 mass %, Cu content is 0.04 to 0.50 mass %, Co content is 1.0 to 3.0 mass %, Ga content is 0.08 to 0.30 mass %, and B content is 0.85 to 0.95 mass %, relative to 100 mass % of a total mass of R, T and B,
• the R-T-B sintered body further includes O,
• O content is 350 ppm or more and 800 ppm or less, relative to a total mass of the R-T-B based permanent magnet,
• an atomic ratio of 14B/(Fe+Co) is more than zero and 1.01 or less,
• R optionally includes a heavy rare earth element which is at least one of Tb and Dy and in a total amount of 0.5 mass % or less when present,
• the R-T-B sintered body has a potential index of from 1,635 or more to 1,673 and a squareness ratio of from 97% to 99.8%, wherein potential index is defined as PI=Br+25×HcJ×4π/2,000;
• Br is a magnitude of a residual magnetic flux density measured by mT unit and HcJ is a coercive force measured by kA/m unit,
• wherein the R-T-B sintered body has the following properties when coated with the coating material and the coated R-T-B sintered body is heat treated to effect grain boundary diffusion of the heavy rare earth element such that a concentration of the heavy rare earth element is reduced from outside to inside:
• the magnet has a potential index of from 1,745 to 1,781 and a squareness ratio of from 90% to 99.1%.