Magnetic Properties of<tex>$hboxTbCu_7$</tex>-Type Sm–Fe–Co–W–M (<tex>$hboxM= $</tex>Nb, Cu, and Cr) System Nitrided Compounds

Abstract

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 TbCu/sub 7/-type structure. The optimum preparation conditions of the compounds were as follows: composition {Sm/sub 10/(Fe/sub 0.95/Co/sub 0.05/)/sub 89.4/W/sub 0.3/Nb/sub 0.3/}/sub 82/ /sub .7/N/sub 17.3/; roller velocity 50 m/s; heat treatment 675/spl deg/C /spl times/ 60 min in high-purity Ar gas; and nitriding condition 420/spl deg/C /spl times/ 15 h in high-purity N/sub 2/ gas. Typical magnetic properties of the obtained powders were as follows: J/sub r/=0.96 T, H/sub cJ/=773.0 kA/m, H/sub cB/=540.4 kA/m, (BH)/sub max/=141.3 kJ/m/sup 3/ (17.8 MGOe), and T/sub c/=493/spl deg/C. Recoil loops of the hysteresis curve and X-ray analysis showed that the sample was an exchange spring magnet. The value of (BH)/sub max/ for the compression-molded isotropic bonded magnet prepared from {Sm/sub 10/(Fe/sub 0.95/Co/sub 0.05/)/sub 89.4/W/sub 0.3/Nb/sub 0.3/}/sub 82/ /sub .7/N/sub 17.3/ powder was 102.1 kJ/m/sup 3/ (12.8 MGOe) when the density of the bonded magnet was 6.1 Mg/m/sup 3/. The reversible temperature coefficient of J/sub r/ was /spl alpha/(J/sub r/)=-0.06%//spl deg/C, and the temperature coefficient of H/sub cJ/ in the range from 25/spl deg/C to 125/spl deg/C obtained by a linear extrapolation was /spl alpha/(H/sub cJ/)=-0.40%//spl deg/C.