• Jardin, R.; Griveau, J.-C.; Prokes, K.; Gofryk, K.; Kolomiets, A.V.; Normile, P.; Heathman, S.; Colineau, E.; Wastin, F.; Rebizant, J.: Magnetic structure and effects of pressure on U4PdGa12. Physical Review B 79 (2009), p. 014409/1-9

10.1103/PhysRevB.79.014409

Abstract:
We report on the magnetic structure, thermopower, compressibility, and electrical resistivity under pressure of the recently discovered heavy-fermion antiferromagnet U4PdGa12. The ordering temperature of the annealed polycrystalline U4PdGa12 is TN~45.5 K. The magnetic structure has been investigated by neutron diffraction. Extra reflections in the powder spectrum appear below ~46 K, in good agreement with macroscopic measurements. The simplest magnetic structure compatible with neutron-diffraction data is a collinear antiferromagnetic structure described by the propagation vector q=[001]. In this case the ordered uranium moment amounts to 1.01(6)µB and point along the a axis. Thermopower confirms the heavy-fermion features in this uranium intermetallic with positive and high values of Seebeck coefficient. The magnetic transition is clearly identified and induces an upturn below 45.5 K which is followed by a continuous decrease in S(T) at lower temperature. Electrical resistivity measurements of U4PdGa12 under pressure of up to 13.5 GPa indicate the disappearance of the magnetic ordering temperature TN around Pc=10 GPa while compressibility measurements performed by x-ray diffraction up to 25 GPa do not show any structural phase transition related to this magnetic collapse. At higher pressure (p>10 GPa) and at low temperature, a non-Fermi-liquid behavior is observed, with a T5/3 dependence of the resistivity. This suggests the possible occurrence of a quantum critical point near Pc.