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

Nanocrystalline SmFe8.95-xGa0.26NbxN delta (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 (Delta Tc = 70 degrees 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 H-cj 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 SmFe9N delta and alpha-Fe can be found. However, an excess of Nb doping may lead to the increase of the weight fraction of alpha-Fe, which in turn deteriorates the magnetic properties. (C) 2018 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.