Functionally graded rare earth permanent magnet

Details Functionally graded rare earth permanent magnet Functionally graded rare earth permanent magnet

2006-01-27

2009-02-10

Sheehan, John P (Department: 1742)

Metal treatment

Stock

Magnetic

C148S301000, C075S232000, C075S236000, C075S244000

Reexamination Certificate

active

07488395

ABSTRACT:
A functionally graded rare earth permanent magnet having a reduced eddy current loss in the form of a sintered magnet body having a composition RaEbTcAdFeOfMgis obtained by causing E and fluorine atoms to be absorbed in a R—Fe—B sintered magnet body from its surface. F is distributed such that its concentration increases on the average from the center toward the surface of the magnet body, the concentration of E/(R+E) contained in grain boundaries surrounding primary phase grains of (R,E)2T14A tetragonal system is on the average higher than the concentration of E/(R+E) contained in the primary phase grains, the oxyfluoride of (R,E) 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, particles of the oxyfluoride having an equivalent circle diameter of at least 1 μm are distributed in the grain boundary region at a population of at least 2,000 particles/mm2, the oxyfluoride is present in an area fraction of at least 1%. The magnet body includes a surface layer having a higher electric resistance than in the interior. In the permanent magnet, the generation of eddy current within a magnetic circuit is restrained.

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