Structure and hard magnetic properties of TbCu7-type SmFe8.95−xGa0.26Nbx nitrides

Nanocrystalline SmFe8.95−xGa0.26NbxNδ (x = 0, 0.1, 0.2, 0.3) were prepared using rapid-quenching, annealing and nitriding. The magnetic properties and crystal structures were systematically studied under various wheel velocities to investigate the influence of Nb doping for the compounds. It is found that TbCu7-type structure is able to be obtained even though the wheel velocity is reduced to 20 m/s (x = 0.3). An significant increase (ΔTc = 70 °C) of the Curie temperature is obtained with Nb doping at x = 0.1 due to the lattice expansion revealed by Rietveld analysis. The optimum coercivity with the value Hcj of 810 kA/m is achieved at x = 0.2 in the nitrides, in which a reasonable distribution of grain sizes of both TbCu7-type SmFe9Nδ and α-Fe can be found. However, an excess of Nb doping may lead to the increase of the weight fraction of α-Fe, which in turn deteriorates the magnetic properties.