R-T-B BASED RARE EARTH PERMANENT MAGNET

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PROBLEM TO BE SOLVED : To provide an R-T-B based sintered magnet which is suitable for a magnetic force-variable motor, and which is small in the falling rate of a coercive force at a high temperature and the falling rate of flatness of a minor curve. SOLUTION : An R-T-B based rare earth permanent magnet has a composition formula represented by (R11-x(Y1-y-zCeyLaz)x)aTbBcMd, where R1 represents one or more rare earth elements, excluding Y, Ce and La, T represents one or more kinds of transition metal including Fe, or a combination of Fe and Co essentially, and M represents Ga, or a combination of Ga and one or more kinds of Sn, Bi and Si; 0.4≤x≤0.7, 0.00≤y+z≤0.20, 0.16≤a/b≤0.28, 0.050≤c/b≤0.070, 0.005≤d/b≤0.028, 0.25≤(a-2c)/(b-14c)≤2.00 and 0.025≤d/(b-14c)≤0.500. The R-T-B based rare earth permanent magnet has main and grain boundary phases of R2T14B type tetragonal crystal. In the R-T-B based rare earth permanent magnet, areal percentages of R-T-M phases, T-rich phases and R-rich phases to an area of all the grain boundary phases are 10.0% or more, 60.0% or less, and 70.0% or less, respectively; and the coverage of the grain boundary phases is 70.0% or more. SELECTED DRAWING : Figure 1 COPYRIGHT : (C)2018, JPO&INPIT