Importance

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Abstract

A rare earth permanent magnet is in the form of a sintered magnet body having a composition R.sup.1.sub.aR.sup.2.sub.bT.sub.cA.sub.dF.sub.eO.sub.fM.sub.g wherein F and R.sup.2 are distributed such that their concentration increases on the average from the center toward the surface of the magnet body, the concentration of R.sup.2/(R.sup.1+R.sup.2) contained in grain boundaries surrounding primary phase grains of (R.sup.1,R.sup.2).sub.2T.sub.14A tetragonal system within the sintered magnet body is on the average higher than the concentration of R.sup.2/(R.sup.1+R.sup.2) contained in the primary phase grains, and the oxyfluoride of (R.sup.1,R.sup.2) is present at grain boundaries in a grain boundary region that extends from the magnet body surface to a depth of at least 20 .mu.m. The invention provides R--Fe--B sintered magnets which exhibit high magnet performance despite minimal amounts of Tb and Dy used.

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First Claim