We report the results of magnetic susceptibility, specific heat, and electrical resistivity measurements on UMGa5 (M=Fe,Co,Ni,Ru,Rh,Pd,Os,Ir,Pt) single crystals. Antiferromagnetic ordering was observed for M=Ni, Pd, and Pt, with ordering temperatures TN=80K, 28K, and 23.5K, respectively. For the UMGa5 compounds with transition metals from the Fe and Co columns, itinerant paramagnetic behavior is observed. The evolution of this behavior is discussed in terms of f-ligand interaction with an emphasis on the role played by f-d hybridization. © 2005 The American Physical Society.

We combine magnetization, pressure-dependent electrical resistivity, and heat capacity measurements to investigate the physical properties of the novel compound UAuBi2. Our single crystals, grown by the self-flux method, share the same tetragonal HfCuSi2-type structure as their Ce-based counterparts. UAuBi2 shows ferromagnetic ordering at Tc=22.5 K, in contrast with the antiferromagnetic transition found in CeAuBi2 (TN=12K) but closely related to UAuSb2 (Tc=31K). Despite the differences, all compounds display an easy axis of magnetization along the c axis and a large magnetocrystalline anisotropy. The heat capacity and pressure-dependent resistivity suggest that UAuBi2 exhibits moderately heavy-fermion behavior (γ∼100mJ/mol·K2) with strongly localized 5f electrons. An intricate competition between crystalline electric field (CEF) effects and two anisotropic exchange interactions (JRKKY) persists in the 5f system, which leads to the striking difference between ground states. A systematic analysis of our macroscopic data using a mean-field model including anisotropic JRKKY interactions and the tetragonal CEF Hamiltonian allows us to extract the CEF scheme and the values of JRKKY. Our results suggest a general trend in this family of compounds and shed light on the similarities and differences between 4f and 5f members.

Measurements of electrical resistivity at applied pressures up to 55 kbar have been carried out on single crystals of the ferromagnet CeNiSb 3 revealing a complex magnetic phase diagram. The ferromagnetism at ambient pressure at T c=6 K first increases with pressure up to 25 kbar, then decreases slightly for P > 25 kbar. In the pressure range 35 kbar≤P≤55 kbar, a second anomaly in the resistivity is found at T M2, below another higher temperature magnetic phase that is conjectured to be different than the ferromagnetism present at lower pressure. Changes in the physical properties such as the residual resistivity, and low temperature maximum in ρ mag(T) suggest a modification of the electronic structure where the two magnetic phases coexist with one another above 35 kbar. The critical pressure for the suppression of the lower temperature phase is estimated to be P cmag2≃55 kbar, while the increase of both the T 2 coefficient of the electrical resistivity A and residual resistivity ρ 0 is suggestive of a quantum critical point associated with the higher temperature magnetic phase at P cmag1∼60 kbar. ©2005 The American Physical Society.

We investigated the effect of electron and hole doping on the high-field low-temperature superconducting state in CeCoIn5 by measuring specific heat of CeCo (In1-x Mx) 5 with M=Sn, Cd, and Hg and x up to 0.33% at temperatures down to 0.1 K and fields up to 14 T. Although both Cd and Hg doping (hole doping) suppresses the zero-field Tc monotonically, Hc2 increases with small amounts of doping and has a maximum around x=0.2% (M=Cd). On the other hand, with Sn doping (electron doping) both zero-field Tc and Hc2 decrease monotonically. The critical temperature for the high-field low-temperature superconducting state correlates with Hc2 and Tc, which we interpret in support of the superconducting origin of this state. © 2010 The American Physical Society.

The physical properties of CeM (In1 - x Hgx)5 (M = Rh, Ir) including specific heat and magnetic susceptibility are reported. Two magnetic phases exist in CeRhIn (In1 - x Hgx)5 with some evidence of a change from incommensurate magnetic order to a commensurate structure near 10% nominal Hg substitution. In CeIr (In1 - x Hgx)5, an antiferromagnetic quantum critical point near x = 3 % (followed by robust long-range antiferromagnetism for x > 5 %) appears to be separated from superconductivity in CeIrIn5. The multitude of magnetic ground states observed in the CeM (In1 - x Hgx)5 materials is quite sensitive to doping and magnetic fields. © 2007.

We report a molten metal flux technique to produce high purity specimens of URu2Si2. Magnetic susceptibility (M/H = x), heat capacity (C) and electrical resistivity (p) measurements show that the bulk properties of these crystals are similar to those that are produced by the Czochralski technique followed by solid-state electro-transport. In particular, we find residual resistivity ratios RRR = p300K /p0 as large as 220.

We report a molten metal flux technique to produce high purity specimens of URu(Formula presented.)Si(Formula presented.). Magnetic susceptibility (Formula presented.)(Formula presented.)(Formula presented.), heat capacity (Formula presented.) and electrical resistivity (Formula presented.) measurements show that the bulk properties of these crystals are similar to those that are produced by the Czochralski technique followed by solid-state electro-transport. In particular, we find residual resistivity ratios RRR (Formula presented.)(Formula presented.)/(Formula presented.) as large as 220. © 2014 © 2014 Taylor & Francis.

We report S 121,123 b nuclear quadrupole resonance (NQR) studies on single crystals of the narrow-gap semiconductor Ce3 Au3 Sb 4. Five NQR lines from the two Sb isotopes were successfully identified. The temperature dependence of the nuclear quadrupole frequency (νQ), as well as the static magnetic susceptibility (χ), is well explained by crystal-electric-field effects. The nuclear spin-lattice relaxation rates (T1-1) of both 121Sb and 123Sb increase rapidly with decreasing temperature. The ratio of T1-1 for the two Sb isotopes is constant at high temperature but it decreases at low temperatures, indicating the role of quadrupole fluctuations of the Ce ions. The possible origin of the large specific heat at low temperatures is discussed basing on our results. © 2010 The American Physical Society.

We show using neutron diffraction that the magnetic structure of CeRhIn4.85 Hg0.15 is characterized by a commensurate propagation vector (1/2,1/2,1/2). This is different from the magnetic structure in the parent compound CeRhIn5, which orders with an incommensurate propagation vector (1/2,1/2,0.297). The special relation between the commensurate magnetic mode and unconventional superconductivity has been shown previously for this class of heavy fermion superconductors. This work provides further evidence for the ubiquity of this antiferromagnetic mode. © 2009 The American Physical Society.

The transverse voltage generated by a temperature gradient in a perpendicularly applied magnetic field, termed the Nernst effect, has promise for thermoelectric applications and for probing electronic structure. In magnetic materials, an anomalous Nernst effect (ANE) is possible in a zero magnetic field. We report a colossal ANE in the ferromagnetic metal UCo0.8Ru0.2Al, reaching 23 microvolts per kelvin. Uranium's 5f electrons provide strong electronic correlations that lead to narrow bands, a known route to producing a large thermoelectric response. In addition, uranium's strong spin-orbit coupling produces an intrinsic transverse response in this material due to the Berry curvature associated with the relativistic electronic structure. Theoretical calculations show that in UCo0.8Ru0.2Al at least 148 Weyl nodes, and two nodal lines, exist within 60 millielectron volt of the Fermi level. This work demonstrates that magnetic actinide materials can host strong Nernst and Hall responses due to their combined correlated and topological nature.