A rare-earth cobalt permanent magnet with good magnetic properties is provided. A rare-earth cobalt permanent magnet contains 23 to 27 mass % R, 3.5 to 5.0 mass % Cu, 18 to 25 mass % Fe, 1.5 to 3.0 mass % Zr in mass and a remainder Co with inevitable impurities, where an element R is a rare earth element at least containing Sm. The rare-earth cobalt permanent magnet has a metal structure including a plurality of crystal grains and a continuously extending grain boundary. A content of Cu in the grain boundary is higher than a content of Cu in the crystal grains, and a content of Zr in the grain boundary is higher than a content of Zr in the crystal grains.

To provide a method for producing surface-modified metal oxide fine particles, which can produce surface-modified metal oxide fine particles having excellent dispersion stability in dispersion liquids having various compositions; a method for producing improved metal oxide fine particles, suitable as a method for producing metal oxide fine particles to be surface-modified in production of the surface-modified metal oxide fine particles; surface-modified metal oxide fine particles which can be produced by the method for producing surface-modified metal oxide fine particles; and a metal oxide fine particle dispersion liquid including the surface-modified metal oxide fine particles. Surface-modified metal oxide fine particles are produced by a method including coating at least a part of surfaces of metal oxide fine particles with a carboxylic acid compound having a certain structure substituted with an amino group which may be cyclic, and/or carboxylate thereof.

A permanent magnet includes a rare earth element R; a transition metal element T; and B. The permanent magnet includes Nd as R. The permanent magnet includes Fe as T. The permanent magnet contains main phase grains and R-rich phases. The main phase grains include R, T, and B. The R-rich phases include R. The main phase grains observed in a cross section of the permanent magnet are flat. The cross section is parallel to an easy magnetization axis direction of the permanent magnet. Each of the R-rich phases is located between the main phase grains. An average value of intervals between the R-rich phases in a direction substantially perpendicular to the easy magnetization axis direction is from 30 μm to 1,000 μm. An average value of lengths of short axes of the main phase grains observed in the cross section is from 20 nm to 200 nm.

Provided is a permanent magnet including a rare-earth element R (such as Nd), a transition metal element T (such as Fe), B, Zr, and Cu. The permanent magnet contains a plurality of main phase grains including Nd, T, and B, and grain boundary multiple junctions, the one grain boundary multiple junction is a grain boundary surrounded by three or more of the main phase grains, one of the grain boundary multiple junctions contains a ZrB.sub.2 crystal and an R—Cu-rich phase including R and Cu, a concentration of B in the one grain boundary multiple junction containing both the ZrB.sub.2 crystal and the R—Cu-rich phase is from 5 to 20 atomic %, a concentration of Cu in the one grain boundary multiple junction containing both the ZrB.sub.2 crystal and the R—Cu-rich phase is from 5 to 25 atomic %, and a surface layer part of the main phase grain includes at least one kind of heavy rare-earth element among Tb and Dy.

A rare earth magnet includes main phase grains having an R.sub.2T.sub.14B type crystal structure. The main phase grains include Ga. A concentration ratio A (A=αGa/βGa) of the main phase grains is 1.20 or more, where αGa and βGa are respectively a highest concentration of Ga and a lowest concentration of Ga in one main phase grain.

A rare earth magnet includes main phase grains having an R.sub.2T.sub.14B type crystal structure. The main phase grains include C. A concentration ratio A1 (A1=αC/βC) of the main phase grains is 1.50 or more, where αC and βC are respectively a highest concentration of C and a lowest concentration of C in one main phase grain.

When sintered magnet bodies 1 are held in a jig 2 having a rotational axis in the vertical direction, immersed in a slurry 41 to apply the slurry thereto, rotated in conjunction with the jig to remove the surplus slurry on the surface of each of the sintered magnet bodies by centrifugal force, and subsequently dried to cause the surfaces of the sintered magnet bodies to be coated with a powder, the slurry is applied while the sintered magnet bodies are held such that no portion of any of the outer surfaces forming the contours of the sintered magnet bodies is orthogonal to the direction of the centrifugal force. As a result, the rare-earth-compound powder can be uniformly applied to the surfaces of the sintered magnet bodies.

A system for producing rare earth magnets from metal powder includes a melting cold hearth atomization system for producing the metal powder from a scrap material and an additive manufacturing system for building the rare earth magnets using the metal powder and an additive manufacturing process. The melting cold hearth atomization system includes a reactor for melting the scrap material into a molten metal, and one or more atomizers for spheroidizing the molten metal into powder particles that form the metal powder. The additive manufacturing system includes magnetized build plates for aligning the grain structures of the rare earth magnets during a building step of the additive manufacturing process. The scrap material can include recycled rare earth magnets, recycled metal powder containing rare earth metal, and recycled rare earth metal parts.

There is provided a method for manufacturing a rare earth sintered magnet by many times repetitively finely pulverizing a rare earth alloy on a jet mill by supplying high-pressure nitrogen gas to narrow grain size distribution to make an easy alignment in a magnetic field, and by micronizing crystal grains by using a hydrogenation-disproportionation-desorption-recombination (HDDR) process, to improve the coercivity and thermostability of the rare earth sintered magnet.

There is provided a method for manufacturing a rare earth sintered magnet to improve the high temperature demagnetization characteristic of the rare earth permanent magnet, by diffusing a heavy rare earth element to the grain boundary of a sintered magnet to improve the magnetic characteristics based on temperature.