Electronic state and magnetism of the rare-earth carbide GdCx (x similar or equal to 0.33)

The electronic state and the magnetism of GdCx (x similar or equal to 0.33) were investigated by the discrete variational (DV)-X alpha calculation method together with those of Gd metal. Magnetic moments on the gadolinium atoms located at the center of the Gd-17 and Gd5C2 clusters extracted from Gd metal and Gd3C were calculated to be 8.38 and 9.70 mu(B), in qualitative agreement with the experimental values (7.96 and 8.28 mu(B) respectively). The exchange splitting of the Gd 4f band in Gd3C was found to increase from that of Gd metal and accounts for the higher Curie temperature of GdCx compounds observed in experiments. The calculated results show that the carbon atoms are charge accepters in these compounds. The higher Curie temperature values (T-c similar or equal to 350 K) observed in the GdCx (x similar or equal to 0.33) compounds compared with Gd metal (T-c = 293 K) are discussed on the basis of the spin-fluctuation theory.