Electronic Specific Heat Associated with Localized States in Actinide Metals

Abstract

Motivated by the observations that the substitution of U for Th in the intermetallic compound ThAl2 results in the formation of localized magnetic moments at the uranium sites, we have made measurements of the low-temperature specific heat of a range of compounds, Th1−xUxAl2, in the temperature range 1.7° to 20°K. We have observed that the value of γ, the electronic contribution, increases with the addition of U; which increases we associate with the formation of localized 5f-like states on the U atoms and close to the Fermi energy. We calculate from the observed values of γ that the change in density of states per U atom ranges from 140 states eV−1 per U atom on the addition of 0.5 at.% U to 80 states eV−1 per U atom on the addition of 18 at.% U. That these states contribute to the specific heat indicates that they form close to the Fermi energy, a condition, within the framework of current theories, favorable to their being magnetized.