Crystal structure and hard magnetic properties of TbCu7-type Sm0.98Fe9.02-xGax nitrides

The compound Sm0.98Fe9.02-xGaxN delta (x=0, 0.25, 0.5, 0.75, 1) were prepared by melt-spun method and subsequent annealing and nitriding. The Rietveld analysis showed that the lattice expansion played an important role in improving the Curie temperature. An obvious development of the Curie temperature was obtained with the increased Ga content from x=0-1 (Delta T-c=90 degrees C). The optimum coercivity of nitrides was obtained at x=0.25 with the value H-cj=652 kA/m (8.15 kOe) after annealing, which corresponded to a reasonable distribution of grain sizes of both TbCu7-type SmFe9N delta and alpha-Fe. However, an excess of Ga doping might lead to an abnormal growth of alpha-Fe, which in turn deteriorated the magnetic properties. It was concluded that a moderate Ga content was very effective in raising the coercivity and Curie temperament in the TbCu7-type Sm-Fe-N.