Hydrogen in actinides: electronic and lattice properties.

Hydrides of actinides, their magnetic, electronic, transport, and thermodynamic properties are discussed within a general framework of H impact on bonding, characterized by volume expansion, affecting mainly the 5states, and a charge transfer towards H, which influences mostly the 6and 7states. These general mechanisms have diverse impact on individual actinides, depending on the degree of localization of their 5states. Hydrogenation of uranium yields UHand UH, binary hydrides that are strongly magnetic due to the 5band narrowing and reduction of the 5-6hybridization.

LaPdIn: superconductivity and lattice properties at ambient and elevated pressures.

Lattice and electronic properties of LaPdIn were studied at ambient and elevated pressures so as to determine features related to a specific atomic coordination without any influence of magnetism. We describe temperature dependences of lattice parameters, heat capacity and electrical resistivity of single-crystalline LaPdIn (s.g.

New type of magnetic structure in the RTX group: TbPdIn.

Anisotropy of bulk magnetic properties and magnetic structure studies of a TbPdIn single crystal by means of bulk magnetization methods and neutron diffraction techniques confirmed the antiferromagnetic order below the Néel temperature 29.5 K. The collinear magnetic structure of Tb magnetic moments aligned along the tetragonal-axis is characterized by a propagation vector= (1/4, 1/4, 1/2), yielding an equal-moment structure with alternating coupling between nearest as well as next-nearest Tb neighbors within the basal plane and antiferromagnetic coupling between the-axis neighbors.

Crystal Structure and Magnetic Properties of Uranium Hydride UH Stabilized as a Thin Film.

A new type of uranium binary hydride, UH, with the CaF crystal structure, was synthesized in a thin-film form using reactive sputter deposition at low temperatures. The material has a grain size of 50-100 nm. The lattice parameter a = (535.

Extended stability range of the non-Fermi liquid phase in UCoAl.

High pressure was used to investigate the stability of the non-Fermi liquid (NFL) state, observed in electrical resistivity of uranium-based band metamagnet UCoAl in a pure form (paramagnet) or with Fe substitution (ferromagnetic ground state), both in a single-crystal form. By combining the pressure variations of magnetization and resitivity in these materials the phase diagram for UCoAl had been constructed. The band metamagnet transforms into the ferromagnetic state as the critical metamagnetic field is reduced to zero by the lattice expansion analogous to the negative pressure.

ThMn-type phases for magnets with low rare-earth content: Crystal-field analysis of the full magnetization process.

Rare-earth (R)-iron alloys are a backbone of permanent magnets. Recent increase in price of rare earths has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. For this reason strong magnets with the ThMn type of structure came into focus.

Electronic properties of PuOs simulating β-Pu: the strongly correlated Pu phase.

We established the basic electronic properties of ζ-PuOs, which is a close analogue to β-Pu, and its low-temperature variety, η-PuOs. Their magnetic susceptibility is 15% higher than for δ-Pu. A specific heat study of ζ-PuOs shows a soft lattice similar to δ-Pu, leading to a low Debye temperature Θ   =  101 K.

UH-based ferromagnets: new look at an old material.

UH is the first discovered material with ferromagnetism based purely on the 5 electronic states, known for more than half century. Although the U metal is Pauli paramagnet, the reduced 5-5 overlap in compounds allows for moment formation and ordering, typically if the U-U spacing exceeds the Hill limit, i.e.

Racah materials: role of atomic multiplets in intermediate valence systems.

We address the long-standing mystery of the nonmagnetic insulating state of the intermediate valence compound SmB6. Within a combination of the local density approximation (LDA) and an exact diagonalization (ED) of an effective discrete Anderson impurity model, the intermediate valence ground state with the f-shell occupation 〈n4f〉 = 5.6 is found for the Sm atom in SmB6.

Synthesis and structural/physical properties of U3Fe2Ge7: a single-crystal study.

A single crystal of U3Fe2Ge7 was synthesized by the tin-flux method, and its structural and electronic properties were studied. The compound crystallizes in the orthorhombic crystal structure of La3Co2Sn7 type with two Wyckoff sites for the U atoms. U3Fe2Ge7 displays a ferromagnetic order below TC = 62 K.

Electronic properties of α-UH stabilized by Zr.

Pure hydride of the α-UH type without any β-UH admixture was prepared by high-pressure hydrogenation of U stabilized by Zr. Such material, characterized by a general formula (UH) Zr , is stable in air at ambient and elevated temperatures. H release is observed between 400-450 °C similar to β-UH.

HOLZ rings in EBSD patterns of the UFeB₄ compound: association with a random distribution of planar defects.

The UFeB₄ phase present in different alloys of the B-Fe-U system was studied by powder X-ray diffraction (PXRD) and scanning electron microscopy complemented with energy-dispersive spectroscopy and electron backscattered diffraction (EBSD). The PXRD data showed that the ternary compound crystallized adopting essentially the YCrB₄-type structure. However, microstructural observations revealed that under high undercooling conditions the UFeB₄ phase exhibits a random distribution of defects parallel to, which are consistently associated with intense higher-order Laue zone rings in EBSD patterns.

Unusual 5f magnetism in the U2Fe3Ge ternary Laves phase: a single crystal study.

Magnetic properties of the intermetallic compound U(2)Fe(3)Ge were studied on a single crystal. The compound crystallizes in the hexagonal Mg(2)Cu(3)Si structure, an ordered variant of the MgZn(2) Laves structure (C14). U(2)Fe(3)Ge displays ferromagnetic order below the Curie temperature T(C) = 55 K and presents an exception to the Hill rule, as the nearest inter-uranium distances do not exceed 3.

Hydrogen induced changes in the crystal structure and magnetic properties of UCoGe.

Hydrogen pressure of 0.5-140 bar has been applied to synthesize hydrides of UCoGe. Besides an α hydride crystallizing in the structure type of the parent compound, which loses the weak ferromagnetism found in pure UCoGe, two distinctly different β hydrides were identified.

Pressure effect on the crystal lattice of unconventional superconductor UCoGe.

High-pressure techniques were used to determine the structural behaviour of the superconducting ferromagnet UCoGe up to 30 GPa enabling us to determine the link between the effect of pressure on the material magnetic properties and crystal structure. The TiNiSi type structure of UCoGe was preserved up to the highest pressure. The a direction, equivalent to the shortest U-U links, was identified as the critical soft direction.

The effect of hydrogenation on magnetic interactions in CeNi.

The crystal structure and magnetic properties of CeNiH(3.7) were studied by means of powder x-ray diffraction, specific heat, and dc and ac magnetization techniques. It was established that hydrogenation stabilizes the 4f(1) state of Ce and turns CeNi-H into a dilute Kondo system with T(K) = 3.

Specific heat of delta-Pu stabilized by Am.

Detailed specific heat C(p) measurements of delta-Pu stabilized by Am (8%-20%) were performed in the temperature range 4.5-300 K. The coefficient of the electronic specific heat gamma, which reflects the quasiparticle density of states at the Fermi level E(F), is smaller than originally assumed and, depending on the estimate of phonon contributions, a value between 35 and 55 mJ/mol K2 can be deduced for Pu-8% Am.

5f-electron localization in PuSe and PuSb.

Thin layers of PuSb and PuSe were studied by photoelectron spectroscopy. X-ray photoelectron spectroscopy and high-resolution valence-band ultraviolet photoelectron spectroscopy spectra show localization of the 5f states and a low density of states at E(F) in PuSb. In PuSe, which can be classified as a heavy fermion system with low carrier density, we observed three narrow peaks in the valence band, which can be related to the 5f emission.