Magnetic characterization of Sm(Fe1-x, Cox)11Ti (x=0, 0.1) determined by heat-capacity measurement from very low to high temperaturese

The thermodynamic and magnetic properties of SmFe11Ti and Sm(Fe0.9Co0.1)11Ti, which are candidates for the main constituents of rare-earth magnets, were investigated by measuring their heat capacities in the range of 2-1050 K. The Curie temperatures, TC, of SmFe11Ti and Sm(Fe0.9Co0.1)11Ti were found to be 582.9 and 705.0 K, respectively. Their magnetic moments, beta, obtained from the magnetic entropies by separating the spin and lattice vibration terms were 20.09 and 22.71 (mu B (compd)-1), respectively, which are consistent with the results of direct magnetization measurements. This indicates that the 3d magnetic moment of Fe, which provides the magnetization, becomes aligned by the effective exchange interaction between Sm 4f via Sm 5d and Fe 3d in a second -order phase transition. In Sm(Fe0.9Co0.1)11Ti, Co 3d strongly exchange-couples with Fe 3d, following the SlaterPauling curves, and TC and beta simultaneously increase. The Sommerfeld parameters of SmFe11Ti and Sm (Fe0.9Co0.1)11Ti indicate the inherent valence fluctuation of Sm; that is, the Sm 4f empty density of states was found to be occupied by the electrons surrounding the Sm atom, indicating low phase stability. These findings are expected to contribute to the design of materials with intrinsic magnetic properties.