Method of producing phosphate-coated SmFeN-based anisotropic magnetic powder and phosphate-coated SmFeN-based anisotropic magnetic powder

A method of producing a phosphate-coated SmFeN-based anisotropic magnetic powder, the method comprising

• performing a phosphate treatment comprising adding an inorganic acid to a slurry containing a SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound containing a rare earth element so that the slurry is adjusted to have a pH of at least 1 and not higher than 4.5 to obtain a phosphate-coated SmFeN-based anisotropic magnetic powder having a surface coated with a phosphate, and
• after the phosphate treatment, heat-treating the phosphate-coated SmFeN-based anisotropic magnetic powder at a temperature of at least 150° C. but not higher than 330° C. in an oxygen-containing atmosphere,
• wherein the rare earth compound is at least one compound selected from the group consisting of a rare earth hydroxide, a rare earth chloride, a rare earth sulfate, a rare earth nitrate, a rare earth acetate, and a combination thereof, and
• wherein the solvent of the slurry is water.