An R-T-B based sintered magnet includes R, T, and B. R represents a rare earth element including at least Tb. T represents a metal element except rare earth elements including at least Fe, Cu, Mn, Al, and Co. B represents boron or boron and carbon. With respect to 100 mass % of a total mass of the R-T-B based sintered magnet, a content of R is 28.0 to 32.0 mass %, a content of Cu is 0.04 to 0.50 mass %, a content of Mn is 0.02 to 0.10 mass %, a content of Al is 0.15 to 0.30 mass %, a content of Co is 0.50 to 3.0 mass %, and a content of B is 0.85 to 1.0 mass %. Tb2/Tb1 is 0.40 to less than 1.0, where Tb1 and Tb2 (mass %) denote a content of Tb at a surface portion and at a core portion, respectively.

The present invention discloses a method of manufacturing, powder making device for rare earth magnet alloy powder, and a rare earth magnet. The method comprises a process of fine grinding at least one kind of rare earth magnet alloy or at least one kind of rare earth magnet alloy coarse powder in inert jet stream with an oxygen content below 1000 ppm to obtain powder that has a grain size smaller than 50 m. Low oxygen content ultra-fine powder having a grain size smaller than 1 m is not separated from the pulverizer, and the oxygen content of the atmosphere is reduced to below 1000 ppm in the pulverizer when crushing the powder. Therefore, abnormal grain growth (AGG) rarely happens in the sintering process. A low oxygen content sintered magnet is obtained and the advantages of a simplified process and reduced manufacturing cost are realized.

Disclosed herein is a method for manufacturing an R-T-B permanent magnet and the magnet made with the method. The method may include preparation of strip pieces by melting and casting, preparing coarse powder by hydrogen decrepitation of the strip pieces; milling the powder into fine powder; pressing the fine powder is pressed to form a compact, pre-sintering the compact in vacuum or inert gas, machining the pre-sintered block to a desired shape; and dispersing the heavy rare earth compound powder into an organic solvent to prepare a slurry and a second sintering step.

The rare-earth sintered magnet has a configuration in which a large number of magnet material particles including a rare-earth substance and each having an axis of easy magnetization have been integrally sintered. The rare-earth sintered magnet is provided with a first surface and a second surface opposing each other in the thickness direction. In a plane in parallel with a width direction and the thickness direction, the magnet material particles are magnetized such that, in a region extending from each of both end portions in the width direction toward the center portion in the width direction, the orientation direction of the easy magnetization axis is gradually changed. A maximum surface magnetic flux density in the first surface and a maximum surface magnetic flux density in the second surface satisfy the relationship (D1/D2)4.

The invention provides a high-performance permanent magnet. The permanent magnet has a composition that is expressed by a composition formula R.sub.pFe.sub.qM.sub.rCu.sub.tCo.sub.100-p-q-r-t, where R is at least one element selected from a rare earth element, M is at least one element selected from the group consisting of Zr, Ti, and Hf, p is a number satisfying 10.8p12.5 atomic percent, q is a number satisfying 25q40 atomic percent, r is a number satisfying 0.88r4.5 atomic percent, and t is a number satisfying 3.5t13.5 atomic percent. The permanent magnet also has a metallic structure that includes a main phase having a Th.sub.2Zn.sub.17 crystal phase, and a Cu-M rich phase having a higher Cu concentration and a higher M concentration than the main phase.

A manufacturing method of a sintered magnet is described. The method includes forming a pre-sintering body from a first magnetic powder and a second magnetic powder (containing a heavy rare earth element, HRE) so that at least part of the second magnetic powder is provided at at least one inner portion of the pre-sintering body and surrounded format least two opposite sides by the first magnetic powder; sintering the pre-sintering body; and annealing the sintered pre-sintering body at an annealing temperature lower than the sintering temperature, thereby causing inter-grain diffusion of HRE from the HRE reservoir zone to the grain boundary phase. After the annealing, the grain boundary phase contains the HRE in a higher concentration than the main phase.

A diffusion treatment device includes: a treatment container including a cylindrical main body and first and second lids, the cylindrical main body having a treatment space which is capable of receiving sintered magnet pieces and RH diffusion sources, the first and second lids being capable of hermetically sealing first and second openings, respectively, at opposite ends of the cylindrical main body; a conveyor for conveying the treatment container by a predetermined distance in an x-axis direction while a longitudinal direction of the treatment container is located in a y-axis direction in a rectangular coordinate system xyz; a heating unit including a lower heating section provided under the treatment container and an upper heating section provided above the treatment container, and a first rotating unit for rotating the treatment container around a y-axis while the longitudinal direction of the treatment container is located in the y-axis direction.

A sintered R1-T-B based magnet work and an R2-Ga alloy are provided. The sintered magnet work contains R: 27.5 to 35.0 mass %, B: 0.80 to 0.99 mass %, Ga: 0 to 0.8 mass %, M: 0 to 2 mass % (where M is at least one of Cu, Al, Nb and Zr), and T: 60 mass % or more. A diffusion step of, while keeping at least a portion of the R2-Ga alloy in contact with at least a portion of a surface of the sintered magnet work, performing a first heat treatment at a temperature which is not lower than 700 C. and not higher than 950 C. to increase the RH amount contained in the sintered magnet work by not less than 0.05 mass % and not more than 0.40 mass %, is performed; and a second heat treatment is performed at a temperature which is not lower than 450 C. and not higher than 750 C. but which is lower than the temperature of the first heat treatment.

Provided is a rare earth sintered magnet in which a multi-layer main phase particle having multiple layers including a layer 1 having R.sup.2 concentration, represented by at %, higher than that of a center of the particle, a layer 2 which is formed on the outside of the layer 1 and has R.sup.2 concentration lower than that of the layer 1, and a layer 3 which is formed on the outside of the layer 2 and has R.sup.2 concentration higher than that of the layer 2 is present at least in a portion in the vicinity of a surface of the main phase particle within at least 500 m from a surface of the sintered magnet body.

When a powder material (5) is molded by introducing the material into a cavity (11) between a lower punch (2) and a die (1), compression molding the material between upper and lower punches (3 and 2) into a compact (51) of desired shape, and moving up the lower punch (2) to eject the compact (51), a lubricant is applied to the interior surface of the die (1) by fitting a pad (24) around the lower punch (2) and impregnating the pad with the lubricant. Since the lubricant is applied on every molding operation, molding operation can be continuously carried out.