Z. Henkie

Non-colinear magnetic structure of U3P4 and U3As4

Abstract Neutron diffraction experiments have been performed on single crystal samples of U3P4 and U3As4. The magnetic ordering is found to be a non-collinear three axial structure in which magnetic moments of U4+ ions are tilted from the [111] axis by an angle of about twenty degrees within (110) planes.

Thermal expansion of skutterudites

The current paper gives an overview of the newly obtained thermal expansion coefficients of skutterudites as well as those so far available in literature. Thermal expansion was determined for CoSb3, Pt4Sn4.4Sb7.6, for As- and Ge-based skutterudites as well as for various high-ZT skutterudites (micro- and nanostructured) with didymium (DD) and mischmetal (Mm) as filler atoms in frameworks of (Fe1−xCox)4Sb12 and (Fe1−xNix)4Sb12, and for double and triple-filled skutterudites such as Ca0.07Ba0.23Co3.95Ni0.05Sb12 and Sr0.025Ba0.075Yb0.1Co4Sb12. For low temperatures, a capacitance dilatometer was used (4–300 K), whereas for temperatures 300<T<750 K, a dynamic mechanical analyzer was employed. For a set of Ge-, P-, and Sb-based skutterudites, lattice parameters of single crystals, measured at three different temperatures, were used to derive the thermal expansion coefficient. The semiclassical model of Mukherjee [Phys. Rev. Lett. 76, 1876 (1996)] has been successfully used to quantitatively describe the thermal...

Evidence for p-f mixing in U3P4 and U3As4 from optical spectroscopy

Abstract The near normal incidence reflectivity of the ferromagnets U 3 P 4 and U 3 As 4 and the isostructural but diamagnetic compounds Th 3 P 4 and Th 3 As 4 has been measured from 0.03 to 12 eV. Trithorium tetraphosphide and tetraarsenide are shown to be indirect gap semiconductors with gap energies of 0.43 and 0.39 eV, respectively. U 3 P 4 and U 3 As 4 display similar sets of p→d transitions than the corresponding thorium compounds, however, they are shifted by 0.85 eV to lower photon energies. It is concluded that the uranium compounds are metals due to a merging of the valence p band into the 6d conduction band giving direct experimental evidence for a p-f mixing effect of the same size. Energy level schemes are derived.

Correlated Electron Phenomena in Ce- and Pr-based Filled Skutterudite Arsenides and Antimonides

In order to elucidate the variety of correlated electron phenomena found in filled skutterudite compounds, experiments were performed on single crystals of ternary Ce- and Pr-based filled skutterudite arsenides LnT 4 As 12 (Ln = Ce, Pr; T = Fe, Ru, Os) and pseudoternary Pr-based skutterudite antimonides Pr(Os 1- x Ru x ) 4 Sb 12 and Pr 1- x Nd x Os 4 Sb 12 . For example, the intermediate valence compound CeRu 4 As 12 exhibits non-Fermi liquid characteristics, while the compounds PrT 4 As 12 display ferromagnetic order (18 K) for T = Fe, BCS superconductivity (2.4 K) for T = Ru, unknown order (2.3 K) and antiferromagnetic order (2.2 K) for T = Os. PrOs 4 As 12 appears to be a Kondo lattice system with a small Kondo temperature (∼ 1 K) and an electronic specific heat coefficient γ∼1 J/mol K 2 . The T – x phase diagrams of Pr(Os 1- x Ru x ) 4 Sb 12 and Pr 1- x Nd x Os 4 Sb 12 reveal regions of superconductivity with different order parameter symmetry and magnetic order.

Crystal growth of uranium and thorium compounds with the elements of group V by chemical vapor transport

Abstract A modification of the Van Arkel method is proposed for purification and growth of single crystals of chemical binary compounds. A quartz bulb with a susceptor heated by a high frequency induction coil is used in this method. The uranium and thorium phosphides, arsenides and antimonides and their solid solution single crystals have been grown. The specific stoichiometry of the crystals can be obtained by heating the susceptor to the appropriate temperature.

Single crystal growth of (rare earth)Me3 compounds where Me ≡ Sn, In and Pb

Abstract Single crystals of (La, Ce, Pr, Nd, Sm, Eu, Gd)Sn 3 , (La, Ce, Pr, Nd, Sm, Gd, Yb, Tm)In 3 and EuPb 3 have been grown from slowly cooled solutions of rare earth metals in Sn, In, and Pb metals, respectively. The cooling rate influenced both the crystal size and the morphology of growth.

Crystal Growth and Properties of the Filled Skutterudite Arsenides

Single crystals of LaOs 4 As 12 , LaOs 4 As 12 , LaOs 4 As 12 , LaOs 4 As 12 PrFe 4 As 12 , PrRu 4 As 12 , PrOs 4 As 12 , and ThFe 4 As 12 were grown from high purity elemental specimens by mineralization in a Cd : As flux. The process was carried out over 3–4 weeks in a sealed quartz ampoule with pressures of 15–40 atm. The elevated pressures were produced by As 4 vapor and Ar gas at the mineralization temperatures between 750–825 °C. To avoid disintegration, the ampoule was heated in a custom built pressure cell. After the synthesis and mineralization were completed, the Cd : As flux components were removed by sublimation and repeatedly used for subsequent crystallizations, thus avoiding dangerous environmental contamination. The morphology and various physical properties of the single crystal filled skutterudite arsenides are presented.

Anisotropies of the electrical resistivity and Hall effect in UAsSe

Abstract We show that anisotropy of the resistivity in UAsSe proves that its total resistivity contains both an isotropic spin disorder component (controlled by RKKY exchange interaction) and an anisotropic single impurity Kondo-like ( T K = 50 K) component. They are present in both paramagnetic and ordered states. This uniaxial and collinear ferromagnet (below 113 K) exhibits high magnetocrystalline anisotropy. Examination of the Hall effect in the paramagnetic phase (up to 430 K) showed that the isotropic normal Hall coefficient R 0 = −8.8×10 −4 cm 3 C −1 (0.47 e − fu −1 in the single band model) is accompanied by a highly anisotropic spontaneous Hall coefficient. This is equal to 0.78 and 3.0 cm 3 C −1 for R s ac and R s ab (magnetic field along the c or b axis) respectively.

Normal state thermopower of the high temperature superconductor YBa2Cu3O6.5+λ

The behaviour of the thermopower between 50 and 350 K has been determined for YBa2Cu3O6.5+λ. A zero value of the thermopower below 90.6 K and a flat maximum of 5.52 μV K−1 at about 100 K have been found. The thermopower shows metal like behaviour. Carrier concentration 2.4 × 1021 cm−3 and carrier mobility 2.5 cm2 V−1 s−1 at ambient temperature were determined.

Non-Fermi liquid behavior in the filled skutterudite compound CeRu4As12

Electrical resistivity ρ, specific heat C, and magnetic susceptibility χ measurements made on the filled skutterudite CeRu4As12 reveal non-Fermi liquid (NFL) T dependences at low T, i.e., ρ(T) ∼ T and weak power law or logarithmic divergences in C(T)/T and χ(T). Measurements also show that the T dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3 and 4 rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3. PACS numbers: 71.10.Hf, 71.28.+dElectrical resistivity ρ, specific heat C, and magnetic M measurements made on the filled skutterudite CeRu4As12 reveal non-Fermi liquid (NFL) temperature dependences at low T, i.e. ρ(T)~T1.4 and weak power law or logarithmic divergences in C(T)/T and M/H = χ(T). Measurements also show that the temperature dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with a nonmagnetic ground state, as revealed by magnetization M(H,T) measurements.