Role of itinerant 5f states on the Fermi surface of Th and possible impurity local moment formation

The nature (itinerant vs localized) of the 5f electrons in the actinides determines their magnetic properties. Extensive optical de Haas--van Alphen data which exist only for Th, the simplest actinide with no occupied 5f states, allow detailed comparisons to be made between theory and experiment. The 5f bands were found, by means of ab initio RAPW energy band calculations, to lie above the Fermi energy, to be itinerant in character, and to significantly affect the reflectivity measurements of Veal, et al. [Phys. Rev. Letters; 30: 1061(1973)]. It is found that the 5f bands when included in the RAPW calculations, give excellent agreement with the de Haas--van Alphen results of Boyle and Gold [Phys. Rev. Letters; 22: 461(1969)], for all sections of the ''lungs'', ''dumbbell'', and ''superegg'' Fermi surfaces, in contrast with calculations based on artificially removing the 5f resonance. Simple overlap charge density impurity scattering potential model calculations are used to discuss the possible occurrence of impurity local moment formation in Th based alloys. (U.S.)