arXiv subjects

U. D. Wdowik

Publications and source records attributed to U. D. Wdowik.

3 recordsLinked to original sources

arXiv2025

Intermediate-valence behavior in U2Rh2Sb

Intermediate-valence behavior is sometimes observed in lanthanide-based materials containing Ce, Yb, Sm or Eu. However, the number of actinide-based systems that exhibit this type of behavior is rather limited. In this work, we present the discovery and characterization of a uranium compound U2Rh2Sb, which turns out to be a candidate for the intermediate-valencebehavior. The material shows a characteristic feature in the magnetic susceptibility around T = 50 K, which can be described within the interconfiguration-fluctuation model of intermediate valence systems. We find the energy difference between the 5f3(U3+) and 5f2(U4+) states to be $δ$Eex/kB $\approx$ 400 K and the corresponding valence fluctuation temperature to be Tvf $\approx$ 140 K. The value of the electronic specific heat coefficient $γ$ = 50 mJ mol-1 U K-2 signals a modest electron effective mass enhancement. The electrical resistivity indicates metallic behavior, albeit with a small residual resistivity ratio. Measurements of thermoelectric properties indicate a change of sign in the Seebeck coefficient around T = 100 K, with a minimum achieved at T = 50 K, which coincides with the broad peak observed in magnetic susceptibility. The experimental results are compared with the theoretical analysis, based on the first-principles calculations, including lattice dynamics.

cond-mat.str-el↗

arXiv2020

Mössbauer studies of spin- and charge-modulations in BaFe2(As1-xPx)2

The BaFe2(As1-xPx)2 compounds with x = 0 (parent), x = 0.10 (under-doped), x = 0.31, 0.33, 0.53 (superconductors with Tc = 27.3 K, 27.6 K, 13.9 K, respectively) and x = 0.70, 0.77 (over-doped) have been investigated versus temperature using 57Fe Mössbauer spectroscopy. Special attention was paid to regions of the spin-density-wave (SDW) antiferromagnetic order, spin-nematic phase, and superconducting transition. The BaFe2(As0.90P0.10)2 compound exhibits a reduced amplitude of SDW as compared to the parent compound and preserved universality class of two-dimensional magnetic planes with one-dimensional spins. The spin-nematic phase region for x = 0.10 is characterized by an incoherent magnetic order. BaFe2(As0.69P0.31)2 shows coexistence of a weak magnetic order and superconductivity due to the vicinity of the quantum critical point. The charge density modulations in the BaFe2(As0.67P0.33)2 and BaFe2(As0.47P0.53)2 superconductors are perturbed near Tc. Pronounced hump of the average quadrupole splitting across superconducting transition is observed for the system with x = 0.33. The phosphorus substitution increases the Debye temperature of the BaFe2(As1-xPx)2 compound. Moreover, experimental electron charge densities at Fe nuclei in this material conclusively show that it should be recognized as a hole-doped system. The measured Mössbauer spectral shift and spectral area are not affected by transition to the superconducting state. This indicates that neither the average electron density at Fe nuclei nor the dynamical properties of the Fe-sublattice in BaFe2(As1-xPx)2 are sensitive to the superconducting transition. Theoretical calculations of hyperfine parameters determining the patterns of Mössbauer spectra of BaFe2(As1-xPx)2 with x = 0, 0.31, 0.5, and 1.0 are performed within the framework of the density functional theory.

cond-mat.supr-con↗

arXiv2015

Phonons in ultrathin oxide films - 2D to 3D transition in FeO on Pt(111)

The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (ML) were studied using the nuclear inelastic scattering (NIS) of synchrotron radiation. Distinct evolution of vibrational characteristics with thickness that is revealed in the phonon density of states (PDOS) witnesses a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low energy part of the PDOS followed a linear dependence in energy that is characteristic for 2-dimensional systems. This dependence gradually transforms with thickness to the bulk ~E-square relation. Density functional theory phonon calculations perfectly reproduced the measured 1 ML PDOS within a simple model of a pseudomorphic FeO/Pt(111) interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long range magnetic order and stabilization of an unusual structural phase.

cond-mat.mtrl-sci↗