Magnetic properties of TbCu7-type Sm-Fe-Co-W-M (M = Nb, Cu, and Cr) system nitrided compounds

This paper reports on experiments on the effect of composition, heat treatment, and nitriding conditions on the magnetic properties of Sm-Fe-Co-W-Nb (Cu, Cr) nitrides with TbCu7-type structure. The optimum preparation conditions of the compounds were as follows: composition {Sm-10(Fe(0.9)5Co(0.05))(89.4)W0.3Nb0.3}(82.7)N-17.3; roller velocity 50 m/s; heat treatment 675degreesC x 60 min in high-purity Ar gas; and nitriding condition 420degreesC x 15 h in high-purity N-2 gas. Typical magnetic properties of the obtained powders were as follows: J(T) = 0.96 T, H-cJ = 773.0 kA/m, HcB = 540.4 kA/m, (BH)(max) = 141.3 kJ/m(3) (17.8 MGOe), and T-c = 493degreesC. Recoil loops of the hysteresis curve and X-ray analysis showed that the sample was an exchange spring magnet. The value of (BH)(max) for the compression-molded isotropic bonded magnet prepared from {Sm-10(Fe0.95Co0.05)(89.4)W0.3Nb0.3}(82.7)N-17.3 powder was 102.1 kJ/m(3) (12.8 MGOe) when the density of the bonded magnet was 6.1 Mg/m(3). The reversible temperature coefficient of J(r) was alpha(J(r)) = -0.06%/degreesC, and the temperature coefficient of H-cJ in the range from 25degreesC to 125degreesC obtained by a linear extrapolation was alpha(H-cJ) = -0.40%/degreesC.