R. Troć

Magnetic properties of UT(Si, Ge) series

Abstract Numerous equiatomic uranium—transition metal ternary compounds of general formula UT(Si, Ge) have been identified in the orthorhombic CeCu 2 -type structure. The magnetic characteristics of these compounds with T = Co, Ni, Ru, Rh, Pd, Ir and Pt have been studied in the range 4.2–300 K. Some systematic dependences in their magnetic behaviour have been revealed. Paramagnetism was observed for UCo(Si, Ge) down to liquid helium temperature. Typical spin-fluctuation susceptibility variation at low temperatures has been found for URu(Si, Ge) and UIrSi. Magnetic ordering was observed for all remaining compounds studied. UNi(Si, Ge) probably show first-order antiferromagnetic transitions, URh(Si, Ge) are itinerant-electron ferromagnets, and UPd(Si, Ge) and UPt(Si, Ge) exhibit some magnetic transitions at low temperatures and behave as local-moment compounds at higher temperature range. The observed magnetic characteristics of the series UT(Si, Ge) reflect the 5f origin of magnetic moment, however more or less influenced by the hybridization between the U-5f and ligand electrons.

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.

On the magnetic ordering in the R2Cu2O5 systems

Abstract We have investigated the magnetic properties of a large group of compounds with the general formula R2Cu2O5, where R stands either for Sc, In and Lu, or the heavy rare-earth element from Tb to Yb. All compounds investigated are isostructural and crystallize in the orthorhombic Ho2Cu2O5 type of crystal structure and show some magnetic transitions at low temperatures. These transitions are mainly associated with the spins on Cu2+ sites. However, a possible magnetic ordering of the rare-earth moments by these ternary oxides has also been discussed.

Preparation and crystal structure of UCuAs2

The structure of the new compound UCuAs2 is determined from single-crystal X-ray analysis. UCuAs2 is tetragonal with space group P4/nmm and a = 3.951(1) A, c = 9.558(3) A, V = 149.3(1) A3 and Z = 2. It is refined to an R value of 0.048 for 271 independent reflections. The structure can be described as the filled ZrSiS-type structure.

Magnetic and transport properties of the UTSn series (T = Co, Ni, Ru, Rh, Pd, Ir and Pt)

Abstract Magnetic susceptibility and electrical resistivity were measured for a series of intermetallic, ternary compounds UTSn, where T stands for Co, Ni, Ru, Rh, Pd, Ir and Pt. For the first time it was shown that UNiSn, except for the well-known cubic MgAgAs-type (low temperature) form, crystallizes also in the orthorhombic CeCu 2 -type (high temperature) form, which probably exhibits the antiferromagnetic properties below 21 K and has a metallic character of conductivity. Also the off-stoichiometric UPt 0.9 Sn 1.1 alloy was found to have two polymorphic forms, where the low temperature form is the MgAgAs-type and shows the complex magnetic properties at low temperatures, while the high temperature one is the Fe 2 P-type, which is ferromagnetic below 28 K. For the remaining UTSn compounds we discuss the differences occurring between our and other authors findings. Especially we emphasize the presence of two magnetic transitions in URhSn; the ferromagnetic one at 17 K and the probably antiferromagnetic one at 52 K. Moreover, two phase transitions of antiferromagnetic character with close lying transition temperatures were found for UPdSn. The obtained experimental results which we analyzed in terms of different crystal structures and the degree of 5f-ligand hybridization which are the main factors influencing the magnetic and transport properties of considered UTSn compounds.

Electrical resistivity investigations of UT(Si,Ge) series

Abstract Low-temperature electrical resistivity measurements were carried out on ternary uranium transition metal silicides and germanides with the general formula UT(Si, Ge), where T = Ni, Ru, Rh, Pd, Ir and Pt. Experimental results pointed out the progression in the magnetic properties from spin-fluctuation systems (URuSi, URuGe, UIrSi), through itinerant-electron ferromagnets (URh(Si, Ge)) and antiferromagnetic phases (UIrGe, UNiGe, UNiSi) to magnetically ordered Kondo compounds (UPtSi, UPdSi, UPdGe, UPtGe). The variation in the ground state properties of this series of compounds is determined mainly by an extent of the hybridization which takes place between the U-5f and ligand electrons and is reflected in their transport properties.

Magnetic susceptibility of the uranium nitrides

Abstract The magnetic susceptibility of UN, and of the higher uranium nitrides has been measured over a wide temperature range, i.e., 4.2–950 K. A large temperature-independent term χ 0 equal to 310 ± 10 × 10 −6 emu/mole has been derived from the total susceptibility data of UN. The obtained χ M values of UN are also related to the Knight shift data from literature. For the higher nitrides U 2 N 3+ x the magnetic susceptibility has been measured for N:U ratios between 1.55 and 1.80. Antiferromagnetic phase transitions have been found for all the examined compositions. The transition temperature T N gradually decreases as the nitrogen content increases, varying from 94 K for UN 1.55 to about 8 K for the maximum composition of UN 1.80±0.02 . The magnetic properties of the higher nitrides are discussed in terms of mixed valency states, either U 4+ and U 6+ or U 4+ and U 5+ for the stoichiometric U 2 N 3 .

Preparation and crystal structure of UCuP2

The compound UCuP2 was prepared in single-crystal form and its crystal structure was determined. UCuP2 crystallizes in the tetragonal system: a = 3.803 A, c = 18.523 A, space group I4/mmm, Z = 4. The structure is considered as a filled UGeTe type with typical layered character. The coordination polyhedra and chemical bonding are discussed.

Magnetic properties of mixed uranium and 3d element chalcogenides of the MU8X17 type

Magnetic susceptibility measurements in the temperature range 4.2–300°K for the MU8X17 type chalcogenides, where M is a 3d transition metal or Mg, and X = S or Se, were carried out. For comparison, the magnetic properties of UTe2 are also given. Almost all the mixed uranium and 3d-transition element chalcogenides are induced-antiferromagnets, as indicated from the occurrence of the susceptibility maxima on the χ vs. T curves and large negative values of the paramagnetic Curie temperatures. The influence of the 3d-transition metals on setting up the magnetic order in the MU8X17-type compounds is discussed.

The electronic structure of UCoGe by ab initio calculations and XPS experiment.

The crystal and electronic structures of the orthorhombic compound UCoGe are presented and discussed. It has been either refined by the x-ray diffraction on a single crystal or computed within the local spin density functional theory, employing the fully relativistic version of the full-potential local-orbital band structure code, respectively. We particularly give our attention to investigating the Fermi surface and de Haas-van Alphen quantities of UCoGe. The calculated electronic density is then examined by x-ray photoelectron spectroscopy (XPS). Fairly good agreement is achieved between theoretical and experimental XPS results in the paramagnetic state. A small difference in the position (in energy scale) of the U 5f bands is caused by the electron localization effect observed in the experimental XPS. There is also some discrepancy for the Co 3d electron contributions below E(F). The Fermi surface in the non-magnetic state is of a semimetallic type while that in the ferromagnetic state, with the ordered moment of -0.47 μ(B)/f.u. along the c axis, is more metallic, with nesting properties that may favour superconductivity.