Functionally graded rare earth permanent magnet

摘要

A functionally graded rare earth permanent magnet is in the form of a sintered magnet body having a composition R<Sup>1</Sup><Sub>a</Sub>R<Sup>2</Sup><Sub>b</Sub>T<Sub>c</Sub>A<Sub>d</Sub>F<Sub>e</Sub>O<Sub>f</Sub>M<Sub>g</Sub> wherein the concentration of R<Sup>2</Sup>/(R<Sup>1</Sup>+R<Sup>2</Sup>) contained in grain boundaries surrounding primary phase grains of (R<Sup>1</Sup>,R<Sup>2</Sup>)<Sub>2</Sub>T<Sub>14</Sub>A tetragonal system within the sintered magnet body is on the average higher than the concentration of R<Sup>2</Sup>/(R<Sup>1</Sup>+R<Sup>2</Sup>) contained in the primary phase grains, R<Sup>2</Sup> is distributed such that its concentration increases on the average from the center toward the surface of the magnet body, the oxyfluoride of (R<Sup>1</Sup>,R<Sup>2</Sup>) is present at grain boundaries in a grain boundary region that extends from the magnet body surface to a depth of at least 20 µm, and the magnet body includes a surface layer having a higher coercive force than in the interior. The invention provides permanent magnets having improved heat resistance.