Abstract: A thermally stable permanent magnet with reduced irreversible loss of flux and improved intrinsic coercivity iHc of 15 KOe or more having the following compositon:(Nd.sub.1-.alpha. Dy.sub..alpha.)(Fe.sub.1-x-y-z Co.sub.x B.sub.y M.sub.z).sub.awherein M represents at least one element selected from the group consisting of Nb, Mo, Al, Si, P, Zr, Cu, V, W, Ti, Ni, Cr, Hf, Mn, Bi, Sn, Sb and Ge, 0.01.ltoreq.x .ltoreq.0.4, 0.04.ltoreq.y.ltoreq.0.20, 0.ltoreq.z.ltoreq.0.03, 4.ltoreq.a.ltoreq.7.5 and 0.03.ltoreq..alpha..ltoreq.0.40. This can be manufactured by (a) sintering an alloy having the above composition by a powder metallurgy method, (b) heating the sintered body at 750.degree.-1000.degree. C. for 0.2-5 hours, (c) slowing cooling it at a cooling rate of 0.3.degree.-5.degree. C./min to temperatures between room temperature and 600.degree. C., (d) heating it at 540.degree.-640.degree. C. for 0.2-3 hours, and (e) rapidly cooling it at a cooling rate of 20.degree.-400.degree. C./min.

Abstract: A process for manufacturing a rare earth-iron-boron alloy permanent magnet by, after sintering, keeping the sintered alloy at temperatures of 750.degree.-1000.degree. C. for 0.2-5 hours, slowly cooling it at a cooling rate of 0.3.degree.-5.degree. C./min. to temperatures between room temperature and 600.degree. C.; annealing it at temperatures of 550.degree.-700.degree. C. for 0.2-3 hours, and rapidly cooling it at a cooling rate of 20.degree.-400.degree. C./min. The permanent magnet contains a matrix, a B-rich phase and a Nd-rich phase. In grain boundaries of the matrix phases covered by bcc phases, thin, fine plates of the bcc phases projecting into the matrix phases are once increased by the first heat treatment and slow cooling and then eliminated by the annealing.

Abstract: A thermally stable permanent magnet with reduced irreversible loss of flux and improved intrinsic coercivity iHc of 15KOe or more having the following composition:(Nd.sub.1-.alpha. Dy.sub..alpha.)(Fe.sub.1-x-y-z Co.sub.x B.sub.y M.sub.z).sub.awherein M represents at least one element selected from the group consisting of Nb, Mo, Al, Si, P, Zr, Cu, V, W, Ti, Ni, Cr, Hf, Mn, Bi, Sn, Sb and Ge, 0.01.ltoreq.x.ltoreq.0.4, 0.04.ltoreq.y.ltoreq.0.20, 0.ltoreq.z.ltoreq.0.03, 4.ltoreq.a.ltoreq.7.5 and 0.03.ltoreq..alpha..ltoreq.0.40. This can be manufactured by (a) sintering an alloy having the above composition by a powder metallurgy method, (b) heating the sintered body at 750.degree.-1000.degree. C. for 0.2-5 hours, (c) slowly cooling it at a cooling rate of 0.3.degree.-5.degree. C./min to temperatures between room temperature and 600.degree. C., (d) heating it at 540.degree.-640.degree. C. for 0.2-3 hours, and (e) rapidly cooling it at a cooling rate of 20.degree.-400.degree. C./min.