| We have discovered that Si substitution is able to stabilize the 2:17 structure of the carbides. A new series, ;The crystal structures, the Curie temperatures, the saturation magnetizations, the temperature dependences of the magnetization, the magnetic anisotropies and the spin reorientation transitions of ;The hyperfine fields, the distribution of Fe and Si atoms on each Fe site and the temperature dependence of the hyperfine parameters have been studied by Mossbauer spectra in an attempt to unravel the magnetic properties of these carbides on an atomic scale. The exchange integrals as a function of the distance between the Fe-Fe pairs have been obtained; the relationships between the Curie temperature and the site occupancy of Si atoms have been found. A negative exchange interaction model is proposed to interpret the origin in the greatly elevated Curie temperature for the nitrides and carbides and to predict the Curie temperatures of... |
