Tdk Corporation

Takurou Iwasa

Masashi Miwa

Ryuji Hashimoto

Masashi Ito

Tamotsu Ishiyama

Haruna Nakajima

A rare-earth sintered magnet contains main phase crystal grains having an Nd5Fe17-type crystal structure, includes R and T (where R represents one or more rare-earth elements that essentially include Sm and T represents Fe or one or more transition metal elements that essentially include Fe and Co), and wherein the compositional ratio of R is 20-40 at % and the remaining portion is substantially T; the remaining portion other than R is substantially only T or only T and C; and when the main phase crystal grains' average grain size in one cross-sectional surface of the rare-earth sintered magnet is defined as Dv, while grain size of individual main phase crystal grains is defined as Di, Dv is at least 1.0 &#x3bc;m, and the main phase crystal grains' area ratio that satisfy 0.7Dv&#x2264;Di&#x2264;2.0Dv is at least 80% with respect to the area of a cross-sectional surface of the rare-earth sintered magnet.

Rare-earth sintered magnet

An R-T-B based permanent magnet includes main phase grains composed of RTB type compound. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. An average grain size of the main phase grains is 0.8 &#x3bc;m or more and 2.8 &#x3bc;m or less. The R-T-B based permanent magnet contains at least C and Zr in addition to R, T, and B. B is contained at 0.75 mass % or more and 0.88 mass % or less. Zr is contained at 0.65 mass % or more and 5.00 mass % or less. A formula (1) of 5.0&#x2264;[B]+[C]&#x2212;[Zr]&#x2264;5.6 is satisfied, where [B] is a B content represented by atom %, [C] is a C content represented by atom %, and [Zr] is a Zr content represented by atom %.

R-T-B based permanent magnet

An R-T-B based permanent magnet includes main phase grains composed of RTB type compound. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. The magnet contains at least C, Ga, and M selected from Zr, Ti, and Nb in addition to R, T, and B. B is contained at 0.71 mass % to 0.88 mass %. C is contained at 0.15 mass % to 0.34 mass %. Ga is contained at 0.40 mass % to 1.40 mass %. M is contained at 0.25 mass % to 2.50 mass %. A formula (1) of 0.14&#x2264;[C]/([B]+[C])&#x2264;0.30 and a formula (2) of 5.0&#x2264;[B]+[C]&#x2212;[M]&#x2264;5.6 are satisfied, where [B], [C], and [M] are respectively a content of B, C, and M by atom %.

An R-T-B based permanent magnet includes R-T-B based compounds as main-phase crystal grains. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. A two-grain boundary is contained between the two adjacent main-phase crystal grains. An average grain size of the main-phase crystal grains is 0.9 &#x3bc;m or more and 2.8 &#x3bc;m or less. A thickness of the two-grain boundary is 5 nm or more and 200 nm or less.

An R-T-B based sintered magnet has a high coercivity even if the carbon content becomes high accompanying the micronization of the finely pulverized particles of the raw material. The R-T-B based sintered magnet includes an R-T-B based compound as main phase grains, wherein, the R-T-B based sintered magnet contains 0.1 mass % to 0.3 mass % of C, and an R&#x2014;Ga&#x2014;C concentrated part exists in the grain boundary formed between or among two or more adjacent main phase grains, and the concentrations of R, Ga and C in the R&#x2014;Ga&#x2014;C concentrated part are higher than those in the main phase grains respectively.

R-T-B based sintered magnet

The present invention provides an R-T-B based sintered magnet having an R-T-B based compound as main phase grains, wherein, the content of Zr contained in the R-T-B based sintered magnet is 0.3 mass % to 2.0 mass %, the main phase grains have Zr, and the R-T-B based sintered magnet have main phase grains with the mass concentration of Zr at the edge portion of the main phase grain being 70% or less of that at the central portion of the main phase grain at the cross-section of the main phase grain.

Growing community of inventors

Tokyo, Japan

Takurou Iwasa