High coercivity in nanocrystalline carbides Sm(Fe,Ga)9C -: art. no. 192503

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 20 to 70 K higher than those of the homologous Sm-2(Fe,Ga)(17) carbides. A record coercivity of 27 kOe is obtained for y=0.25 with annealing temperature of the noncarbonated powder at 710 degrees C which corresponds to an optimal grain size around 28 nm. The M-R/M(90 kOe) ratio of 0.57 combined with high coercivity and high T-C makes this alloy suitable for permanent magnet applications. (C) 2005 American Institute of Physics.