High coercivity in nanocrystalline carbides Sm(Fe,Ga)9C
Résumé
The structural and magnetic properties of metastable hexagonal SmFe9−yGayC compounds, with y=0.25, 0.5, 0.75, and 1, have been investigated by means of powder x-ray diffraction, magnetic measurements, and high-resolution transmission electron microscopy. After carbonation, the Rietveld analysis points out an anisotropic lattice expansion more important for the carbon site. The Curie temperatures are systematically 20to70K higher than those of the homologous Sm2(Fe,Ga)17 carbides. A record coercivity of 27kOe is obtained for y=0.25 with annealing temperature of the noncarbonated powder at 710°C which corresponds to an optimal grain size around 28nm. The MR∕M(90kOe) ratio of 0.57 combined with high coercivity and high TC makes this alloy suitable for permanent magnet applications.