| 简介 |
PROBLEM TO BE SOLVED : To prevent coloring of the surface of a permanent magnet and deterioration in magnetic characteristics of the permanent magnet when bringing out the permanent magnet consisting of a sintered magnet with Dy and Tb diffused in a crystal grain boundary phase at the time of pressure release.
SOLUTION : The iron-boron-rare earth sintered magnet is disposed in a treatment chamber 20 in vacuum and is heated to a predetermined temperature. In the same or another treatment chamber, a metal evaporation material containing Dy and/or Tb is disposed and heated for evaporation. The evaporated Dy and/or Tb metal atoms are made to attach to the surface of the sintered magnet in a controlled amount, and the attached metal atoms are diffused in the crystal grain boundary phase of the permanent magnet before a thin film made of the metal evaporation material is formed on the surface of the sintered magnet. Then, an inactive gas with a lower concentration of oxygen than that of the atmosphere is introduced into the treatment chamber in vacuum to oxidize the surface of the sintered magnet with Dy and/or Tb diffused in the crystal grain boundary phase and the inside of the treatment chamber, and then the pressure is released.
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