Magnetic Properties of TbCu₇-Type Sm-Fe-Co-W System Nitriding Compounds

Abstract

Experiments were carried out to investigate the magnetic properties of Sm-Fe-Co-W system nitriding compounds with TbCu₇-type structure. Sm_y(Fe_0.95Co_0.05)_100-x-yW_x(x=0-1.0, y=8-11) alloy ribbons were prepared by the single roller rapid-quenching method, and the effects of alloy composition, and conditions of heat-treatment and nitrogenation, were examined with regards to their magnetic properties. The optimum preparation conditions of the compounds are as follows. Composition: {Sm₁₀(Fe_0.95Co_0.05)_89.7W_0.3}_85.0N_15.0, roller velocity: 50 m/s, heat treatment: 675°C×60 min in high-purity Ar gas, and nitriding condition: 400°C×15 h in high-purity N₂ gas. Typical magnetic properties of the obtained compound powders are H_cJ=765.7 kA/m (9.62 kOe), J_r=0.93 T (96.40 emu/g), (BH)_max=134.5 kJ/m³ (16.9 MGOe), and T_c=480°C. It was found that this sample was an exchange spring magnet from TEM photographs and recoil loops of the hysteresis curve. The value of (BH)_max for the compression-molded isotropic bonded magnet prepared from the: {Sm₁₀(Fe_0.95Co_0.05)_89.7W_0.3}_85.0N_15.0 powder is 95.0 kJ/m³ (12.0 MGOe), when the density of bonded magnet is 6.1 Mg/m³. And the reversible temperature coefficient of J_r is α(J_r)=-0.071 %/°C, the temperature coefficient of H_cJ in the range from 25°C to 125°C obtained by a linear extrapolation is α(H_cJ)=-0.42%/°C.