PROCESS FOR PRODUCTION OF SURFACE-MODIFIED RARE EARTH SINTERED MAGNETS AND SURFACE-MODIFIED RARE EAR

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The invention provides a rare earth sintered magnet which is improved in corrosion resistance by oxidizing heat treatment to such a level as to exhibit satisfactory corrosion resistance even in an atmosphere of varying humidity and which is reduced in the deterioration of magnetic characteristics due to oxidizing heat treatment and a process for the production of the magnet. A surface-modified rare earth sintered magnet characterized in that the surface modified part is an at least three-layered surface modification layer which comprises a main layer containing R, Fe, B and oxygen, an amorphous layer containing at least R, Fe and oxygen, and an outermost layer containing hematite-base iron oxide as the main constituent in this order from the inside of the magnet; and a process for the production of the magnet, characterized by comprising the step of subjecting a magnet body to heat treatment in an atmosphere of oxygen partial pressure of 1 Œ 102 to 1Œ 105Pa and water vapor partial pressure of 0.1 to 1000Pa (exclusive of 1000Pa) at 200 to 600°C.