Heavy-Fermion and Semiconducting Properties of the Ternary Uranium Compounds U₃T₃Sn₄and U₃T₃Sb₄(T=Ni, Cu, Pd, Pt and Au)

Abstract

We present results of magnetic, transport and calorimetric measurements on U 3 T 3 X 4 with T=Ni, Cu, Pd, Pt and Au and X=Sn and Sb. A heavy-fermion behavior manifests itself in U 3 T 3 Sn 4 , where the electronic specific-heat coefficient increases from 90 mJ/K 2 mol U for T=Ni and Pt to about 300 mJ/K 2 mol U for T=Cu and Au. We ascribe the mass enhancement to the dehybridization of 5 f electrons with the d electrons derived from the T atom. On the other hand, U 3 T 3 Sb 4 with T=Ni, Pd and Pt shows a semiconducting behavior with a band gap of about 0.2 eV, whereas U 3 Cu 3 Sb 4 is a metallic ferromagnet with T c =91 K. In these antimonides, 5 f electrons are localized because of the weak hybridization with the 5 p electrons from the Sb atom. These results indicate that the number of 5 p electrons in the present system determines whether the system shows heavy-fermion or semiconducting behavior.