An RFeB system sintered magnet which does not contain a heavy rare-earth element R.sup.H (Dy, Tb and Ho) in a practically effective amount and yet is suited for applications in which the magnet undergoes a temperature increase during its use. The RFeB system sintered magnet contains at least one element selected from the group consisting of Nd and Pr as a rare-earth element R in addition to Fe and B while containing none of Dy, Tb and Ho, the magnet having a temperature characteristic value t.sub.(100-23) which satisfies −0.58<t.sub.(100-23)<0, where t.sub.(100-23) is defined by the following equation:

[00001]$t_{\left(100-23\right)}=\frac{H_{\mathrm{cj}}\left(100\right)-H_{\mathrm{cj}}\left(23\right)}{\left(100-23\right)\times H_{\mathrm{cj}}\left(23\right)}\times 100$

using H.sub.cj(23) which is the value of the coercivity at a temperature of 23° C. and H.sub.cj(100) which is the value of the coercivity at a temperature of 100° C.

A strip cast alloy containing Nd in excess of the stoichiometry of Nd.sub.2Fe.sub.14B is subjected to HDDR treatment and diffusion treatment, yielding microcrystalline alloy powder in which major phase crystal grains with a size of 0.1-1 μm are surrounded by Nd-rich grain boundary phase with a width of 2-10 nm. The powder is finely pulverized, compacted, and sintered, yielding a sintered magnet having a high coercivity.

A method for producing a magnet powder is provided in the present disclosure. The method includes synthesizing a R—Fe—B-based magnet powder by a reduction-diffusion process, coating an antioxidant film onto a surface of the R—Fe—B-based magnet powder, and immersing and cleaning the R—F—B-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 method for manufacturing a sintered magnet according to one embodiment of the present disclosure is provided. The method includes producing an R-T-B-based magnetic powder through a reduction-diffusion method, and sintering the R-T-B-based magnetic powder, wherein R is a rare earth element, and T is a transition metal, and wherein the producing the magnetic powder includes adding a refractory metal sulfide powder to a R-T-B-based raw material.

The present invention relates to a method for preparing a neodymium-iron-boron rare-earth permanent magnetic material, in particular to a hot press molding-based method for preparing a rare-earth permanent magnet. The problem that the residual magnetism and coercive force of a rare-earth permanent magnet prepared in the prior art cannot be both high is solved. An RTM alloy infiltrates same during an HD treatment. RTM sticks to the surface of coarse powder and infiltrates into the interior of the coarse powder along a grain boundary. The temperature of hot press sintering is relatively low, and grains barely grow. In the absence of Dy and Tb, a higher coercive force is obtained. If an alloy containing Dy and Tb is used for infiltration, these atoms diffuse into the surface layer of a main phase during preheating and heat treatment, achieving grain boundary hardening. Under the premise of a very small reduction in the residual magnetism, the coercive force is greatly improved.

The present invention relates to a Ce-containing sintered rare earth permanent magnet with high toughness and high coercivity and a method of preparing the magnet, belonging to the technical field of rare earth permanent magnetic materials. The magnet is prepared by steps of raw material batching, strip casting, hydrogen decrepitation and jet milling, powder orientating and forming, sintering and heat treatment. The materials of the permanent magnet comprise the main phase alloy powders and the Ce added phase alloy powders, wherein the Ce added phase alloy is a magnetic phase or a non-magnetic liquid-phase alloy; and the Ce added phase alloy accounts for 5% to 30% of the total weight of the permanent magnet, and the remainder is the main phase alloy. During the jet milling stage, a certain concentration of oxygen is added into the inert gas, so that the final magnet has an oxygen content of 1500 to 2500 ppm. The Ce-containing dual-alloy magnet prepared in accordance with the present invention has high coercivity, and the intrinsic coercivity (H.sub.cj) is up to 17 to 28.73 kOe. The magnet of the present invention has good fracture toughness which is increased by 10% to 30% as compared with the conventional Nd—Fe—B sintered magnet. The magnet of the present invention can meet needs of high-end applications such as wind power generation, new energy vehicles, and the like, and greatly expands the application fields of Ce-containing magnets.

An object of the present invention is to enhance a coercive force of magnetic particles by promoting formation of a continuous R-rich grain boundary phase in a crystal grain boundary of a magnetic phase of the particles, and to thereby obtain R-T-B-based rare earth magnet particles further having a high residual magnetic flux density. The present invention relates to production of R-T-B-based rare earth magnet particles capable of exhibiting a high coercive force even when a content of Al therein is reduced, and a high residual magnetic flux density, in which formation of an R-rich grain boundary phase therein can be promoted by heat-treating Al-containing R-T-B-based rare earth magnet particles obtained by HDDR treatment in vacuum or in an Ar atmosphere at a temperature of not lower than 670° C. and not higher than 820° C. for a period of not less than 30 min and not more than 300 min.

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 obtaining high coercivity.

The present invention provides R-T-B-based rare earth magnet particles comprising no expensive rare resources such as Dy and having an excellent coercive force which can be produced by HDDR treatment without any additional steps. The present invention relates to R-T-B-based rare earth magnet particles comprising crystal grains comprising a magnetic phase of R.sub.2T.sub.14B, and a grain boundary phase, in which the grain boundary phase has a composition comprising R in an amount of not less than 13.5 atom % and not more than 35.0 atom % and Al in an amount of not less than 1.0 atom % and not more than 7.0 atom %. The R-T-B-based rare earth magnet particles can be obtained by controlling heat treatment conditions in the DR step of the HDDR treatment in the course of subjecting a raw material alloy to the HDDR treatment.

A rare earth sintered magnet is prepared by a method comprising the steps of melting raw materials to form an alloy, pulverizing the alloy into a fine powder, shaping the fine powder into a compact, and sintering the compact. The pulverizing step includes a coarse pulverizing step including hydrogen decrepitation and a fine pulverizing step, and further includes the step of adding a lubricant. The sintering step includes an atmosphere heat treatment including heating the compact at a temperature from the lubricant decomposition temperature to the sintering temperature and holding at the temperature for a time, in an inert gas atmosphere, and a vacuum heat treatment. The sintered magnet has a low impurity concentration and a narrow carbon concentration distribution.