Dualism of the 5felectrons of the ferromagnetic superconductor UGe2as seen in magnetic, transport, and specific-heat data

Abstract

Single-crystalline UGe${}_{2}$ was investigated by means of magnetic susceptibility, magnetization, electrical resistivity, magnetoresistivity, and specific-heat measurements, all carried out in wide temperature and magnetic-field ranges. An analysis of the obtained data points out the dual behavior of the 5$f$ electrons in this compound, i.e., possessing simultaneously local and itinerant characters in two substates. The magnetic and thermal characteristics of the compound were modeled using the effective crystal field (CF) in the intermediate coupling scheme and initial parameters obtained in the angular overlap model. Various configurations of the localized 5${f}^{n}$ ($n$ $=$ 1, 2, and 3) electrons on the uranium ion have been probed. The best results were obtained for the 5${f}^{2}$ (U${}^{4+})$ configuration. The CF parameters obtained in the paramagnetic region allowed us to reproduce satisfactorily the experimental findings in the whole temperature range including also the magnitude of the ordered magnetic moment of uranium at low temperature. The electrical resistivity data after subtraction of the phonon contribution reveal the presence of a Kondo-like interaction in UGe${}_{2}$ supporting the idea of partial localization of the 5$f$ electrons in UGe${}_{2}$. On the other hand, magnetoresistivity and an excess of specific heat originated from the hybridized (itinerant) part of 5$f$ states, apparent around the characteristic temperature ${T}^{*}$, give a distinct signature for the presence of the coupled charge-density wave and spin-density wave fluctuations over all the ferromagnetic region with a maximum at ${T}^{*}$, postulated earlier in the literature.