UNUSUAL MAGNETIC, TRANSPORT AND THERMODYNAMICAL PROPERTIES OF THE URANIUM TERNARIES UNISN, UPDIN AND UNIGA

We present our recent results of systematic experimental work on magnetic, transport and thermodynamical properties of the equiatomic ternaries UNiSn, UPdIn and UNiGa. UNiSn with cubic MgAgAs-type structure exhibits a semi-conductor-to-metal transition associated with a type-I antiferromagnetic ordering. Both UPdIn and UNiGa crystallize in the hexagonal ZrNiAl-type structure. UPdIn is the first example of a two-dimensional heavy-fermion system accompanied by a pseudogap formation along the c-axis due to the development of the c-axis modulated magnetic structure. UNiGa exhibits a giant magnetoresistance being as large as DELTArho/rho congruent-to 90% at T = 1.5 K for the current parallel to the c-axis, which is a result of the antiferromagnetic-to-ferromagnetic transition occurring at B=0.7 T. All of these unusual physical properties can be a consequence of the change in the hybridization of the highly correlated 5f-electrons with s, p or d electron states by the development of magnetic ordering or the magnetic order-order transition.