Itinerant ferromagnetism in actinide 5f-electron systems: Phenomenological analysis with spin fluctuation theory
AbstractWe have carried out an analysis of magnetic data in 69 uranium, 7 neptunium, and 4 plutonium ferromagnets with the spin fluctuation theory developed by Takahashi [Y. Takahashi, J. Phys. Soc. Jpn. 55, 3553 (1986)JUPSAU0031-901510.1143/JPSJ.55.3553]. The basic and spin fluctuation parameters of the actinide ferromagnets are determined and the applicability of the spin fluctuation theory to actinide 5f system has been discussed. Itinerant ferromagnets of the 3d transition metals and their intermetallics follow a generalized Rhodes-Wohlfarth relation between peff/ps and TC/T0, viz., peff/ps∝(TC/T0)−3/2. Here, ps, peff, TC, and T0 are the spontaneous and effective magnetic moments, the Curie temperature, and the width of spin fluctuation spectrum in energy space, respectively. The same relation is satisfied for TC/T0<1.0 in the actinide ferromagnets. However, the relation is not satisfied in a few ferromagnets with TC/T0∼1.0 that corresponds to local moment system in the spin fluctuation theory. The deviation from the theoretical relation may be due to several other effects not included in the spin fluctuation theory such as the crystalline electric field effect on the 5f electrons from ligand atoms. The value of the spontaneous magnetic moment ps increases linearly as a function of TC/T0 in the uranium and neptunium ferromagnets below (TC/T0)kink=0.32±0.02, where a kink structure appears in relation between the two quantities. ps increases more weakly above (TC/T0)kink. A possible interpretation with the TC/T0 dependence of ps is given.