Magnetic Properties of Melted ThMn₁₂-Type Carbides and Their Nitrides

The carbides of NdDy_0.2Fe_12-yMo_yC_0.6 (y=1.5, 2) crystallized in the ThMn₁₂-type structure have been successfully synthesized by arc melting method, followed by a heat treatment. The magnetic properties are strongly enhanced with the addition of carbon. Upon the carbonation the saturation magnetization M_s is increased by about 20emu/g and the Curie temperature T_c is enhanced by 40--70K. The spin reorientation (SR) temperature decreases from 125 K for NdDy_0.2Fe₁₀Mo₂ to 55 K for NdDy_0.2Fe₁₀Mo₂C_0.6 indicating the change of magnetocrystalline anisotropy in the Nd sublattice. It is found that the intrinsic magnetic properties of the carbides can be improved by further nitrogenation. The composite carbon--nitrogen compounds show a T_c～560K, M_s～105emu/g and H_a (anisotropy field) ～86kOe for NdDy_0.2Fe₁₀Mo₂C_0.6N_z and a T_c～628K, M_x～119emu/g and H_a～115kOe for NdDy_0.2Fe_10.5Mo_1.5C_0.6N_z. These magnetic properties are even better than those of simple nitrides, suggesting that these compounds can be considered as a good candidate for permanent magnet applications.