FUNCTIONALLY GRADED RARE EARTH PERMANENT MAGNET

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PURPOSE : A functionally graded rare earth permanent magnet is provided to have both high electric resistance and magnetic characteristic. CONSTITUTION : A functionally graded rare earth permanent magnet is a sintered magnet body having a composition of RaEbTcAdFeOfMg(1) or (R.E)a+bTcAdFeOfMg(2). R1 is one or more than two kinds selected from rare earth elements including Sc and Y, E is one or more than two kinds selected from alkaline earth metal elements and rare earth elements, R and E contain the same element and the formula(1) is the case when the R and E do not contain the same element and the formula(2) is the case when the R and E contain the same element, T is one or two kinds selected from Fe and Co, A is one or two kinds selected from B and C, M is one or two kinds selected from Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, and W, and a - g are atom percents of alloy and are in a range of 10<=a<=15 and 0.005<=b<=2 in case of formula(1) or 10.005<=a+b<=17 in case of formula(2), 3<=d<=15, 0.01<=e<=4, 0.04<=f<=4, 0.01<=g<=11 and c is a balance. The F is distributed so that the average concentration gets denser as goes from the center of the magnet body to the surface of the magnet body. In a grain boundary unit surrounding a columnar grain composed of a (R, E)2T14A tetragon, the concentration of E/(R+E) included in a grain boundary is averagely denser than that of E/(R+E) of the main phase grain. The acid fluoride of (R, E) exists in the grain boundary unit to a depth of at least 20um from the surface of the magnet body of the grain boundary unit. The particle of the acid fluoride having a diameter corresponding to a circle of 1um is distributed at a ratio of 2000/mm2, and the acid fluoride occupies over 1 percent in an area friction. The electric resistance of a surface layer of the magnet body is higher than that of the inside of the magnet body. © KIPO 2006