Rare earth sintered magnet, method for producing same, motor and automobile

Abstract

A rare earth sintered magnet 10 including a magnet body that includes a rare earth compound, and a protective layer on the magnet body, having a first layer and a second layer in that order from the magnet body side, wherein the surface portion of the magnet body has a higher heavy rare earth element content than the interior of the magnet body that is surrounded by the surface portion, the first layer includes a rare earth oxide, the mass ratio of the heavy rare earth element being 1 or greater with respect to the light rare earth element, and the second layer includes an oxide containing iron and/or boron which is different from the rare earth oxide, the second layer having a lower rare earth oxide content than the first layer.

1 - 8 . (canceled) 
     
     
         9 . A method for producing a rare earth sintered magnet, comprising:
 a diffusion step in which a heavy rare earth compound is adhered onto the surface portion of a magnet body including a rare earth compound and is heated so that the heavy rare earth element in the heavy rare earth compound is diffused throughout the surface portion of the magnet body while a covering layer including the heavy rare earth compound is formed on the magnet body;   a surface treatment step in which at least part of the surface portion of the covering layer is removed; and   an oxidizing treatment step in which the covering layer is oxidized in an oxidizing atmosphere including an oxidizing gas, to form a protective layer including, in an order as seen from the magnet body side, a first layer including a rare earth oxide, the mass ratio of the heavy rare earth element being 1 or greater with respect to the light rare earth element, and a second layer including an oxide including at least one of iron and boron and having a lower rare earth oxide content than the first layer.   
     
     
         10 . The method for producing a rare earth sintered magnet according to  claim 9 , wherein in the diffusion step, the heavy rare earth compound-adhered magnet body is heated to between 600° C. and 1000° C. 
     
     
         11 . The method for producing a rare earth sintered magnet according to  claim 9 , wherein in the surface treatment step, at least part of the surface portion of the covering layer is removed to lower the arithmetic mean roughness Ra of the covering layer to no greater than 2 μm. 
     
     
         12 . The method for producing a rare earth sintered magnet according to  claim 9 , wherein the heavy rare earth compound is a heavy rare earth element hydride. 
     
     
         13 . The method for producing a rare earth sintered magnet according to  claim 10 , wherein in the surface treatment step, at least part of the surface portion of the covering layer is removed to lower the arithmetic mean roughness Ra of the covering layer to no greater than 2 μm. 
     
     
         14 . The method for producing a rare earth sintered magnet according to  claim 10 , wherein the heavy rare earth compound is a heavy rare earth element hydride. 
     
     
         15 . The method for producing rare earth sintered magnet according to  claim 13 , wherein the heavy rare earth compound is a heavy rare earth element hydride.