An application step of applying an adhesive agent to an application area of a surface of a sintered R-T-B based magnet, an adhesion step of allowing a particle size-adjusted powder that is composed of a powder of an alloy or a compound of a heavy rare-earth element RH which is at least one of Dy and Tb to adhere to the application area of the surface of the sintered R-T-B based magnet, and a diffusing step of heating it at a temperature which is equal to or lower than a sintering temperature of the sintered R-T-B based magnet to allow the heavy rare-earth element RH contained in the particle size-adjusted powder to diffuse from the surface into the interior of the sintered R-T-B based magnet are included. The particle size of the particle size-adjusted powder is set so that, when powder particles composing the particle size-adjusted powder are placed on the entire surface of the sintered R-T-B based magnet to form a single particle layer, the amount of heavy rare-earth element RH contained in the particle size-adjusted powder is in a range from 0.6 to 1.5% with respect to the sintered R-T-B based magnet by mass ratio.

In at least one embodiment, a single sintered magnet is provided having a concentration profile of heavy rare-earth (HRE) elements within a continuously sintered rare-earth (RE) magnet bulk. The concentration profile may include at least one local maximum of HRE element concentration within the bulk such that a coercivity profile of the magnet has at least one local maximum within the bulk. The magnet may be formed by introducing alternating layers of an HRE containing material and a magnetic powder into a mold, pressing the layers into a green compact, and sintering the green compact to form a single, unitary magnet.

Provided are a rare-earth permanent magnet whose magnet density after sintering is very high and a method for manufacturing a rare-earth permanent magnet. Thus, a magnet raw material is milled into magnet powder, and then, a compound 12 is formed by mixing the magnet powder thus milled with a binder. Next, the compound 12 thus formed is subjected to a hot-melt molding onto a supporting substrate 13 so as to form a green sheet 14 molded to a sheet-like shape. Thereafter, while the green sheet 14 thus molded is softened by heating, magnetic field orientation is carried out by applying a magnetic field to the green sheet 14 thus heated; and further, the green sheet 14 having been subjected to the magnetic field orientation is calcined by a vacuum sintering, which is further followed by a pressure sintering to produce a permanent magnet 1.

The present invention provides an R-T-B based sintered magnet having excellent corrosion resistance together with good magnetic properties. The R-T-B based sintered magnet contains R.sub.2T.sub.14B crystal grains, wherein, an RGaCoCuN concentrated part exists in a grain boundary formed between or among two or more adjacent R.sub.2T.sub.14B crystal grains, and the concentrations of R, Ga, Co, Cu and N in the RGaCoCuN concentrated part are higher than those in the R.sub.2T.sub.14B crystal grains respectively.

A ferrite sintered magnet includes a composition expressed by a formula (1) of Ca.sub.1-w-xLa.sub.wA.sub.xFe.sub.zCo.sub.mMn.sub.aO.sub.19. In the formula (1), w, x, z, m, and a satisfy a formula (2) of 0.21w0.62, a formula (3) of 0.02x0.46, a formula (4) of 7.43z11.03, a formula (5) of 0.18m0.41, and a formula (6) of 0.046a0.188. In the formula (1), A is at least one kind of element selected from a group consisting of Sr and Ba.

A manufacturing method of rare earth magnet based on heat treatment of fine powder includes the following: an alloy for the rare earth magnet is firstly coarsely crushed and then finely crushed by jet milling to obtain a fine powder; the fine powder is heated in vacuum or in inert gas atmosphere at a temperature of 100 C.1000 C. for 6 minutes to 24 hours; then the fine powder is compacted under a magnet field and is sintered in vacuum or in inert gas atmosphere at a temperature of 950 C.1140 C. to obtain a sintered magnet; and machining the sintered magnet to obtain a magnet; then the magnet performs a RH grain boundary diffusion at a temperature of 700 C.1020 C. An oxidation film forms on the surface of all of the powder.

A manufacturing method of an alloy powder for rare earth magnet and the rare earth magnet based on heat treatment includes the following: an alloy of the rare earth magnet is firstly coarsely crushed and then finely crushed by jet milling to obtain a fine powder; the fine powder is obtained by being heated in vacuum or in inert gas atmosphere at a temperature of 100 C.1000 C. for 6 minutes to 24 hours. The heat treatment of fine powder is performed after the process of finely crushed jet milling before the process of compacting under a magnetic field, so that the sintering property of the powder is changed drastically, and it obtains a magnet with a high coercivity, a high squareness and a high heat resistance.

A manufacturing method includes: manufacturing a sintered compact having a composition of (Rl).sub.x(Rh).sub.yT.sub.zB.sub.sM.sub.t; manufacturing a precursor by performing hot deformation processing on the sintered compact; and manufacturing a rare earth magnet by performing an aging treatment on the precursor in a temperature range of 450 C. to 700 C. In this method, a main phase thereof is formed of a (RlRh).sub.2T.sub.14B phase. A content of a (RlRh).sub.1.1T.sub.4B.sub.4 phase in a grain boundary phase thereof is more than 0 mass % and 50 mass % or less. Rl represents a light rare earth element. Rh represents a heavy rare earth element. T represents a transition metal. M represents at least one of Ga, Al, Cu, and Co. x, y, z, s, and t are percentages by mass of Rl, Rh, T, B, and M. x, y, z, s, and t are expressed by the following expressions: 27x44, 0y10, z=100xyst, 0.75s3.4, 0t3.

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.

The present invention provides a permanent magnet with both a high corrosion resistance and magnetic properties compared to the existing R-T-B based magnets. It is a R-T-B based sintered magnet (wherein, R includes Y (yttrium) and R1 as essential, R1 is at least one kind of rare earth elements except Y but includes Nd as essential, and T is at least one kind of transition metal element including Fe or the combination of Fe and Co as essential). By allowing the ratio of R1 to Y (R1:Y) in the R contained in the grain boundary phase to be 80:2035:65 in terms of the calculated molar ratio of the grain boundary phase and adding Y to the raw materials of the R-T-B based magnet, Y segregates at the triple point, and corrosion of grain boundary phase is prevented by oxidized Y.