A method for producing a sintered rare-earth magnet characterized by sintering a raw material that includes a ribbon-shaped polycrystalline phase with an average grain size of 10 to 200 nm fabricated by rapid solidification of an alloy melt having a rare-earth magnet composition, and a low-melting point phase formed on the surface of the polycrystalline phase and having a melting point lower than the polycrystalline phase.

The present invention relates to surface-treated rare earth-based magnetic particles comprising rare-earth-based magnetic particles, a first coating layer comprising a phosphoric acid compound which is formed on a surface of the respective magnetic particles and a second coating layer in the form of a composite coating film comprising a silicon compound and a phosphoric acid compound which is formed on a surface of the first coating layer, wherein an amount of Fe eluted from the rare earth-based magnetic particles is not more than 10 mg/L; a resin composition for bonded magnets comprising the above surface-treated rare earth-based magnetic particles and a resin; and a bonded magnet comprising the above surface-treated rare earth-based magnetic particles.

A method for producing a magnet powder is provided in the present disclosure. The method includes synthesizing a RFeB-based magnet powder by a reduction-diffusion process, coating an antioxidant film onto a surface of the RFeB-based magnet powder, and immersing and cleaning the RFB-based magnet powder in an aqueous solvent or a non-aqueous solvent, wherein R is Nd, Pr, Dy or Tb, and wherein the antioxidant film includes a compound containing at least one amino group.

A magnet preparation method includes coating powder slurry on at least one of a first surface or a second surface of an NdFeB matrix and carrying out a curing reaction, to obtain a coated magnet, and subjecting the coated magnet to a vacuum heat treatment, a grain boundary diffusion treatment, and an aging treatment. The first surface and the second surface are opposite to each other. The powder slurry includes powder containing heavy rare earth element and UV monomer. The UV monomer includes radical-cured UV monomer. A temperature of the vacuum heat treatment is in a range from 250 C. to 600 C.