Permanent magnet and method of producing permanent magnet

Abstract

A permanent magnet has a grain structure that includes a main phase and a grain boundary phase that is primarily composed of a first metal. A second metal that enhances the coercivity of the permanent magnet and a third metal that has a lower standard free energy of oxide formation than the first metal and the second metal are diffused in the permanent magnet, and the third metal is present in the form of an oxide in the grain boundary phase.

1 . A production method of a permanent magnet, comprising:
 a first step of preparing a sintered magnet that has a grain structure that includes a main phase and a grain boundary phase which is primarily composed of a first metal, and   a second step of diffusing both a third metal that has a lower standard free energy of oxide formation than the first metal and a second metal that has a higher standard free energy of oxide formation than the third metal and that enhances the coercivity of the permanent magnet, into the grain boundary phase from surfaces of the sintered magnet, and then forming oxide of the third metal in the grain boundary phase;   wherein the second metal does not form an oxide; and   wherein the third metal is not present in the main phase at the first step.   
     
     
         2 . The production method of the permanent magnet according to  claim 1 , wherein the second step includes:
 a third step of diffusing the third metal into the grain boundary phase to form an intermediate; and   a fourth step of diffusing the second metal into the grain boundary phase of the intermediate.   
     
     
         3 . The production method of the permanent magnet according to  claim 2 ,
 wherein the fourth step is a step that includes forming a layer of the second metal over surfaces of the intermediate by sputtering and carrying out a heat treatment to diffuse the second metal into the grain boundary phase.   
     
     
         4 . The production method of the permanent magnet according to  claim 2 ,
 wherein the fourth step is a step that includes applying vapor of the second metal to surfaces of the intermediate to diffuse the second metal into the grain boundary phase.   
     
     
         5 . The production method of the permanent magnet according to  claim 1 , wherein the second step includes:
 forming a layer of the third metal over surfaces of the sintered magnet;   depositing a layer of the second metal on the layer of the third metal; and   carrying out a heat treatment of the sintered magnet covered with the layers of the second metal and the third metal to diffuse the second metal and the third metal into the grain boundary phase.   
     
     
         6 . The production method of the permanent magnet according to  claim 5 ,
 wherein the layer of the third metal and the layer of the second metal are deposited by sputtering.   
     
     
         7 . The production method of the permanent magnet according to  claim 1 , wherein the second step includes:
 depositing a layer of an alloy of the second metal and the third metal over the surfaces of the sintered magnet; and   carrying out a heat treatment to diffuse the alloy into the grain boundary phase.   
     
     
         8 . The production method of the permanent magnet according to  claim 7 , wherein the layer of the alloy of the third metal and the second metal is deposited by sputtering. 
     
     
         9 . The production method of the permanent magnet according to  claim 1 , wherein the first metal is neodymium or praseodymium. 
     
     
         10 . The production method of the permanent magnet according to  claim 9 , wherein the second metal is any one of dysprosium, terbium or holmium, and the third metal is either yttrium or scandium. 
     
     
         11 . The production method of the permanent magnet according to  claim 1 ,
 wherein the concentration of oxygen in the permanent magnet is 0.2% by mass or smaller.   
     
     
         12 - 16 . (canceled)