A motor rotor includes an iron core. A mounting groove is recessed from an end surface of the iron core and extends in a direction from a middle of the iron core to an outer peripheral surface of the iron core. The motor rotor further includes a first magnet and a second magnet embedded in the mounting groove and arranged at an interval along an extension direction of the mounting groove. The first magnet is fixed at a radial outer side of the second magnet. A magnetization direction of each of the first magnet and the second magnet is perpendicular to the extension direction of the mounting groove. A coercive force of the first magnet being greater than a coercive force of the second magnet.

A method for producing an RFeB system sintered magnet according to the present invention includes: a process (S1) of preparing a lump of HDDR-treated raw material alloy that contains a polycrystalline substance including crystal grains having an average grain size of 1 μm or less in terms of an equivalent circle diameter calculated from an electron micrograph image, by an HDDR treatment including steps of heating a lump of RFeB system alloy containing 26.5 to 29.5% by weight of the rare-earth element R, in a hydrogen atmosphere at a temperature between 700 and 1,000° C., and changing the atmosphere to vacuum while maintaining the temperature within a range from 750 to 900° C.; a process (S2) of preparing a lump of raw material alloy having a high rare-earth content by heating the lump of HDDR-treated raw material alloy at a temperature between 700 and 950° C. in a state where the HDDR-treated raw material alloy is in contact with a contact substance including a second alloy that contains the rare-earth element R at a higher content ratio than a content ratio of the rare-earth element R in the RFeB system alloy; a process (S3) of preparing raw material alloy powder by fine pulverization of the lump of raw material alloy having a high rare-earth content into powder having an average particle size of 1 μm or less; an orienting process (S4) including steps of placing the raw material alloy powder in a mold, and applying a magnetic field to the raw material alloy powder without conducting compression molding; and a sintering process (S5) including a step of heating the oriented raw material alloy powder at a temperature between 850 and 1,050° C.

A sintered magnet contains Sm—Fe—N-based crystal grains and has high coercivity; and a magnetic powder is capable of forming a sintered magnet without lowering the coercivity even if heat is generated in association with the sintering. A sintered magnet comprises a crystal phase composed of a plurality of Sm—Fe—N-based crystal grains and a nonmagnetic metal phase present between the Sm—Fe—N crystal grains adjacent to each other, wherein a ratio of Fe peak intensity I.sub.Fe to SmFeN peak intensity I.sub.SmFeN measured by an X-ray diffraction method is 0.2 or less. A magnetic powder comprises Sm—Fe—N-based crystal particles and a nonmagnetic metal layer covering surfaces of the Sm—Fe—N crystal particles.

Provided are an anisotropic rare earth sintered magnet having a ThMn.sub.12-type crystal compound as a main phase and exhibits good magnetic characteristics, and a method for producing it. The anisotropic rare earth sintered magnet has a composition of a formula (R.sub.1-aZr.sub.a).sub.v(Fe.sub.1-bCo.sub.b).sub.100-v-w-x-y(M.sup.1.sub.1-cM.sup.2.sub.c).sub.wO.sub.xC.sub.y (where R is one or more kinds selected from rare earth elements and indispensably includes Sm, M.sup.1 is one or more kinds of elements selected from the group consisting of V, Cr, Mn, Ni, Cu, Zn, Ga, Al, and Si, M.sup.2 is one or more kinds of elements selected from the group consisting of Ti, Nb, Mo, Hf, Ta, and W, and v, w, x, y, a, b, and c each satisfy 7≤v≤15 at %, 4≤w≤20 at %, 0.2≤x≤4 at %, 0.2≤y≤2 at %, 0≤a≤0.2, 0≤b≤0.5, and 0≤c≤0.9), which contains a main phase of a ThMn.sub.12-type crystal compound in an amount of 80% by volume or more with the average crystal particle diameter of the main phase being 1 μm or more, which contains an R oxycarbide in the grain boundary area, and which has a density of 7.3 g/cm.sup.3 or more. The production method for the anisotropic rare earth sintered magnet includes grinding an alloy that contains a ThMn.sub.12-type crystal compound phase but does not contain an oxycarbide, then molding it in a mode of pressure powder molding with magnetic field application thereto to give a molded article, and thereafter sintering it at a temperature of 800° C. or higher and 1400° C. or lower to form an oxycarbide in the grain boundary area.

A method for producing a powdered starting material, which is provided for production of rare earth magnets, including includes the following steps: pulverizing an alloy, including at least one rare earth metal, wherein a powdered intermediate product is formed from the alloy including the at least one rare earth metal, and carrying out at least one classification aimed at particle size and/or particle density for the powdered intermediate product. A fraction of the powdered intermediate product, which is formed by the at least one classification, is used for fabrication of rare earth magnets. Furthermore, at least one dynamic classifier is provided, implementing at least one classification directed at particle size and/or particle density for the powdered intermediate product and thereby separates the fraction from the powdered intermediate product, which forms the starting material for manufacturing rare earth magnets.

This sintered R-T-B based rare-earth magnet includes: R.sub.2Fe.sub.14B type compound crystal grains, including a light rare-earth element RL (which includes at least one of Nd and Pr) as a major rare-earth element R, as main phases; and a heavy rare-earth element RH (which includes at least one of Dy and Tb). Before its surface region is removed, the sintered R-T-B based rare-earth magnet has no layer including the rare-earth element R at a high concentration in that surface region. The sintered R-T-B based rare-earth magnet has a portion in which coercivity decreases gradually from its surface region toward its core portion. The difference in the amount of TRE between a portion of the sintered R-T-B based rare-earth magnet that reaches a depth of 500 μm as measured from its surface region toward its core portion and the core portion of the sintered R-T-B based rare-earth magnet is 0.1 through 1.0.

A method for producing a NdFeB system sintered magnet. The method includes: a hydrogen pulverization process, in which coarse powder of a NdFeB system alloy is prepared by coarsely pulverizing a lump of NdFeB system alloy by making this lump occlude hydrogen; a fine pulverization process, in which fine powder is prepared by performing fine pulverization for further pulverizing the coarse powder; a filling process, in which the fine powder is put into a filling container; an orienting process, in which the fine powder in the filling container is oriented; and a sintering process, in which the fine powder after the orienting process is sintered as held in the filling container. The processes from hydrogen pulverization through orienting are performed with neither dehydrogenation heating nor evacuation each for desorbing hydrogen occluded in the hydrogen pulverization process. The processes from hydrogen pulverization through sintering are performed in an oxygen-free atmosphere.

A step of, while an RLM alloy powder (where RL is Nd and/or Pr; M is one or more elements selected from among Cu, Fe, Ga, Co, Ni and Al) and an RH oxide powder (where RH is Dy and/or Tb) are present on the surface of a sintered R-T-B based magnet, performing a heat treatment at a sintering temperature of the sintered R-T-B based magnet or lower is included. The RLM alloy contains RL in an amount of 50 at % or more, and the melting point of the RLM alloy is equal to or less than the temperature of the heat treatment. The heat treatment is performed while the RLM alloy powder and the RH oxide powder are present on the surface of the sintered R-T-B based magnet at a mass ratio of RLM alloy:RH oxide=9.6:0.4 to 5:5.

A method for producing a permanent or soft magnet including the following steps: a) providing: a solution containing a solvent in which are dispersed a set of objects which possess a permanent magnetic moment; a substrate on which are fixed to the surface or within a cavity that it may have, a 1st pad and a 2nd pad, said 1st pad includes a face facing and parallel to a face that the 2nd pad includes; b) the solution is deposited on the surface of the substrate or, as the case may be, within its cavity; c) the substrate is placed in a magnetic field so that the set of objects are grouped together between the face of the 1st pad and the face of the 2nd pad so as to form a permanent magnet.

A two-step diffusion method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet belongs to the preparing technical field of rare earth permanent magnet materials. The compositions of the two main phase alloys are RE-Fe—B (RE is Nd or Pr) and (Nd, MM)-Fe—B (MM is mischmetal), respectively. First, PrHoFe strip-casting alloy is used as a diffusion source. Next, a PrHo-rich layer is uniformly coated on the surface of (Nd, MM)-Fe—B hydrogen decrepitation powders. The higher anisotropic fields of Pr.sub.2Fe.sub.14B and Ho.sub.2Fe.sub.14B are used to improve the coercivity. Then, the ZrCu strip-casting alloy is used as a diffusion source. A Zr-rich layer is uniformly coated on the surface of the powders after the first-step diffusion, which prevents the growth of the MM-rich main phase grains during the sintering process and the inter-diffusion between the two main phases, thus obtains high coercivity.