Valence band of Ce2Co0.8Si3.2Ce_{2}Co_{0.8}Si_{3.2} and Ce2RhSi3Ce_{2}RhSi_{3} studied by resonant photoemission spectroscopy and FPLO calculations

This work presents studies of the valence band of two Kondo lattice systems: Ce2Co0.8Si3.2, which is paramagnetic with the Kondo temperature T-K approximate to 50 K and Ce2RhSi3, which is antiferromagnetic below T-N = 4.5 K and exhibits TK approximate to 9 K. The photoemission spectra, which are obtained with photon energy tuned to Ce - 4d 4f resonance, reveal a Kondo peak at the Fermi energy (E-F), its spin orbit splitting partner at 0.24 eV and a broad maximum related to Ce f(0) final state. The spectra indicate that Kondo peak has a higher intensity for Ce2Co0.8Si3.2. The off-resonance photoemission data reveal that a maximum in the 3d electron density of states is shifted towards EF for Ce2Co0.8Si3.2 as compared to Ce2RhSi3. Full-potential local-orbital calculations were realized with local spin density approach +U approach for 213 stoichiometry. They show that a higher density of states near EF is observed for Ce2CoSi3. The calculations also reveal the existing tendencies for antiferromagnetic and ferromagnetic ground states in a case of Ce2RhSi3 and Ce2CoSi3, respectively

Ferromagnetism in structurally disordered UFe0.39Ge2

International audienceA polycrystalline sample of the uranium ternary germanide UFe0.39Ge2 was examined by means of X-ray powder diffraction, DC magnetization and AC magnetic susceptibility, heat capacity and electrical resistivity measurements performed in wide ranges of temperature and magnetic fields. The experiments confirmed that the compound crystallizes with orthorhombic crystal structure of the CeNiSi2-type that is closely re-lated to that of the ferromagnetic superconductor UGe2 and orders ferromagnetically at 37 K. Moreover, it exhibits some features characteristic of ferromagnetic cluster glasses. The electrical transport in UFe0.39Ge2 is strongly influenced by structural disorder arising from the partly occupied Fe-sites in its crystallographic unit cell. (C) 2021 The Author(s). Published by Elsevier B.V. CC_BY_NC_ND_4.

Metamagnetic transition in single-crystalline UIr 2_{2} 2 Si 2_{2} 2

Abstract A single crystal of the ternary uranium silicide UIr $$_{2}$$ 2 Si $$_{2}$$ 2 was studied by means of of X-ray diffraction, magnetization, heat capacity and electrical transport measurements. The studied compound orders antiferromagnetically at the Néel temperature of 5.5 K and undergoes a metamagnetic transition at 1.8 K in a field of 1.52 T. The metamagnetic transition has a spin-flop character

Superconductivity in the Einstein Solid VAl10.1

We used magnetic susceptibility, resistivity, and heat capacity measurements to characterize the superconducting state in the Einstein solid VAl10.1. We find that VAl10.1 is a weak–coupling, type–II superconductor with Tc = 1.53 K and an upper critical field of Hc2(0) = 800 Oe. The heat capacity data in the range 0.07 < T < 1.53 K are consistent with an isotropic energy gap of Δ0 = 0.23 meV.JRC.E.6-Actinide researc

Antiferromagnetic Kondo Lattice NpNi2Sn

The compound NpNi2Sn has been studied by means of x-ray diffraction, heat capacity, magnetic and electrical transport measurements performed over a wide range of temperatures and applied magnetic fields. The results revealed Kondo lattice behavior and antiferromagnetic ordering below the Néel temperature of 13 K. The compound has been characterized as a moderately enhanced heavy-fermion system, one of very few known amidst Np-based intermetallics.JRC.E.6-Actinides researc

Competition of Magnetocrystalline Anisotropy of Uranium Layers and Zig-Zag Chains in UNi0.34_{0.34}Ge2_2 Single Crystals

Structural and thermodynamic properties of single-crystalline UNi$_{1-x}$Ge$_2$ with $x$\,=\,0.66 have been investigated by measuring magnetization, specific heat, and thermal expansion over a wide range of temperatures and magnetic fields. The measurements revealed the emergence of a long-range antiferromagnetic ordering of uranium magnetic moments below the N{\'e}el temperature $T_{\rm N}$\,=\,45.5\,K and the existence of two easy axes in the studied compound, namely $b$ and $c$, which correspond to the planes of the uranium zig-zag chains. Magnetic field applied along these two crystallographic directions induces in the system a first-order metamagnetic phase transition (from antiferromagnetism to field-polarized paramagnetism), and the width of the magnetic hysteresis associated with that transition reaches as much as 40 kOe at the lowest temperatures. A magnetic phase diagram developed from the experimental data showed that the metastable region associated with that magnetic hysteresis forms a funnel that narrows toward the N{\'e}el point in zero magnetic field. The four-layer Ising model has successfully predicted the collinear antiferromagnetic structure in UNi$_{0.34}$Ge$_2$ (known from earlier reports), its magnetic phase diagram, and temperature and field variations of its magnetization. Moreover, it suggests that the first-order phase transition extends down to zero magnetic field, although it is barely detectable in the experiments performed in low magnetic fields. According to this model, the second-order phase transition occurs in the compound only in zero field.Comment: 15 pages, 12 figure

Competition of magnetocrystalline anisotropy of uranium layers and zigzag chains in UNi0.34Ge2 single crystals

International audienceStructural and thermodynamic properties of single-crystalline UNi1-xGe2 with x = 0.66 have been investigated by measuring magnetization, specific heat, and thermal expansion over a wide range of temperatures and magnetic fields. The measurements revealed the emergence of a long-range antiferromagnetic ordering of uranium magnetic moments below the Neel temperature T-N = 45.5(1) K and the existence of two easy axes in the studied compound, namely, b and c, which correspond to the plane of the uranium zigzag chains. Magnetic field applied along these two crystallographic directions induces in the system a first-order metamagnetic phase transition (from antiferromagnetism to field-polarized paramagnetism), and the width of the magnetic hysteresis associated with that transition reaches as much as about 40 kOe at the lowest temperatures. A magnetic phase diagram developed from the experimental data showed that the metastable region associated with that magnetic hysteresis forms a funnel that narrows toward the Neel point in a zero magnetic field. The four-layer Ising model has successfully predicted the collinear antiferromagnetic structure in UNi0.34Ge2 (known from earlier reports), its magnetic phase diagram, and temperature and field variations of its magnetization. Moreover, it suggests that the first-order phase transition extends down to a zero magnetic field, although it is barely detectable in the experiments performed in low magnetic fields. According to this model, the second-order phase transition occurs in the compound only in a zero field

New insights into the crystal structure of UTE0.25Ge2=U4TGe8 (TE = Ru, Os) and ferromagnetic properties of the Os-bearing uranium germanide

International audienceA single crystal of the compound previously described as &quot;URu0.25Ge2&quot; was studied by means of transmission electron microscopy and synchrotron X-ray diffraction (XRD) measurements. The experiments revealed that the deficient ruthenium atoms order to a superstructure of the CeNiSi2 structure-type with space group P21/n (no. 14) and cell parameters a' = 5.7422(7) angstrom, b' = 15.931(2) angstrom, c' =11.4903(9) angstrom and beta' = 90.755(8)degrees, corresponding to the Tb4FeGe8-type structure. In addition, a new isostructural compound, U4OsGe8, was synthesized and charac-terized by powder X-ray diffraction, electron diffraction, DC magnetization, AC susceptibility, electrical resistivity and specific heat measurements. The experiments showed that it crystallizes with the monoclinic, ordered P21/n unit cell with lattice parameters a' = 5.7438(1) angstrom, b' = 15.9355(1) angstrom, c' = 11.4586(1) angstrom and beta' = 90.681(1)degrees, and orders ferromagnetically at about 54 K, which is clearly seen in all the physical properties studied. Moreover, its electrical resistivity was found to exhibit features characteristic of semimetals, and the electron contribution to the specific heat is moderately enhanced, as in all other known phases of the UTE1-xGe2 (with TE = transition element) family of compounds

Observation of topological nodal fermion semimetal phase in ZrSiS

Unveiling new topological phases of matter is one of the current objectives in condensed matter physics. Recent experimental discoveries of Dirac and Weyl semimetals prompt to search for other exotic phases of matter. Here we present a systematic angle-resolved photoemission spectroscopy (ARPES) study of ZrSiS, a prime topological nodal semimetal candidate. Our wider Brillouin zone (BZ) mapping shows multiple Fermi surface pockets such as the diamond-shaped Fermi surface, ellipsoidal-shaped Fermi surface, and a small electron pocket encircling at the zone center (Γ) point, the M point and the X point of the BZ, respectively. We experimentally establish the spinless nodal fermion semimetal phase in ZrSiS, which is supported by our first-principles calculations. Our findings evidence that the ZrSiS-type of material family is a new platform to explore exotic states of quantum matter, while these materials are expected to provide an avenue for engineering two-dimensional topological insulator systems

From antiferromagnetic and hidden order to Pauli paramagnetism in UM2Si2 compounds with 5f electron duality

Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U 5f electrons in UM2Si2 (M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U 5f(2) configuration with the Gamma((1))(1) and Gamma(2) quasi-doublet symmetry. The amount of the U 5f(3) configuration, however, varies considerably across the UM2Si2 series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in UPd2Si2 and UNi2Si2, the availability of orbital degrees of freedom needed for the hidden order in URu2Si2 to occur, as well as the appearance of Pauli paramagnetism in UFe2Si2. A unified and systematic picture of the UM2Si2 compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered ThCr2Si2 structure