O. Vogt

Kondo behaviour of the electrical resistivity in USb and UTe

Abstract We report electrical resistivity measurements in pseudobinary USbxTe1−x compounds in a wide temperature range. The unambiguous Kondo behaviour of metallic UTe is numerically analyzed. The electrical resistivity of semimetal-like USb can be described by a Kondo term plus a decreasing resistivity contribution due to the thermal activation of f electrons into the d band.

New ferromagnetic europium compounds

Abstract Eu3P2 and Eu3As2 are new ferromagnetic semiconductors crystallizing in the Ba3P2 structure. Their Curie points are 25° and 18°K, respectively.

Evidence for a valence transition in UxY1-xSb

Electrical, optical and lattice-constant measurements on single crystalline UxY1-xSb (x=0, 0.01, 0.03, 0.08, 0.15, 0.20, 0.30, 0.70 and 1) reveal a nonmagnetic U 5f2 singlet groundstate for x ⩽ 0.15, a lowering of the f3→f2d1 transition energy with decreasing x for x > 0.15 and a marked anomaly of the lattice parameter for x ≅ 0.15. These results as well as the anomalous concentration dependence of the U moment can be described by a valence transition of U at a concentration of about 15% U (x = 0.15).

Transport studies of Kondo behavior, ferromagnetic and antiferromagnetic order in U1−xThxSb

Abstract We report electrical resistivity, Hall effect and magnetization measurements in the system U 1−x Th x Sb for magnetic fields up to 100 kOe. In U 0.14 Th 0.86 Sb a Kondo-like behavior of the resistivity is detected and the interaction J df between the conduction d electrons and the uranium f electrons is found to be about −0.2 eV. The dilution of USb by ThSb leads to large modifications of the electrical transport properties, reflecting the change from antiferromagnetism to ferromagnetism and simultaneously a decrease of the ordered magnetic moment per uranium atom occurs. A simple model is presented which accounts for this decrease assuming that all the conduction electrons added by thorium are polarized antiparallel to the remaining uranium f electrons due to the negative J df . The Kondo temperature is used to estimate the band width and the binding energy of the 5f state.

Localized versus itinerant 5f electrons: A comparative study of USb and UO2

Abstract The near normal incidence reflectivity of USb single crystals has been measured for photon energies from 0.03 to 11 eV. An energy level scheme is derived. Comparison with the corresponding results for UO 2 reveals for USb a hybridization of the 5 f and 6 d wave functions and a delocalization of 5 f electrons. An estimate of the free carrier concentration indicates that USb has a non integer number of f electrons.

Crystal-field splitting in CexY1−x Sb and CexLa1−x Sb

Abstract We report measurements of the crystal-field splitting of Ce 3+ by inelastic neutron scattering in Ce 0.5 Y 0.5 Sb and by high field anisotropic magnetization measurements for Ce 0.1 Y 0.9 Sb and Ce 0.1 La 0.9 Sb. These measurements together with the earlier neutron scattering study of CeSb by Rainford et al indicate that there is at most a small variation of crystal-field splitting with Ce concentration, and consequently with lattice constant; and that this crystal-field splitting is somewhere between 15 and 25°K at low temperature.

Modification of the magnetic structure of UAs — Appearance of an incommensurate phase below TN in UAs0.97Se0.03, studied by neutron diffraction from a single crystal

Abstract The magnetic structure of UAs0.97Se0.03 has been studied by neutron diffraction from a single crystal in zero applied magnetic field. It is found to be antiferromagnetic, of type-IA (++--) below To = 75.6 K and of type-I (+-+-) above To. The type-I persists till TIC = 113.5 K, while above it and up to TN = 122 K an incommensurate phase appears, thereby modifying the magnetic structure in pure UAs. The k-value of the wavevector K (along cubic axes) is changing from 0.642 at TN to 0.652 at TIC. The transitions at To and TIC are first-order while the transition at TN is second-order. The ordered magnetic moment is 2.15 μB at T = 4.2 K, it varies smoothly to 1.95 μB at T = 75.4 K and drops drastically to 1.47 μB at T = 76 K.

Magneto-optical response of f- and d-states in uraniummonosulfide☆

Abstract High field magnetooptic Kerr-rotation and -ellipticity measurements in the energy range between 0.55 and 5.1 eV are reported for a 5f-metal for the first time. The remarkable size of the magneto-optical response is explained with the large overlap of f-and d-orbitals and the enhanced spin-orbit energies in heavy atoms. The diagonal as well as the off-diagonal conductivity is discussed in a microscopic model. We obtain a conduction band occupancy of 1.1 d-electrons per uranium ion with a negative spin-polarization of -42%. The spin-polarization of the f-electrons is found to be 62%.

Magnetic properties of the system Zn1−xCdxCr2Se4

Abstract Magnetic susceptibilities and magnetic moments of the systems Zn 1− x Cd x Cr 2 Se 4 have been measured.

A heat-treatment method to minimize the infrared absorption in EuTe

Abstract Non-stoichiometric EuTe single crystals synthetized from the elements and grown by sublimation show a strong free-carrier absorption in the near-infrared. A re-sublimation of the excess component controlled by measurements of infrared absorption yields a purely divalent residue having an outstanding transparency in the visible and the near-infrared spectral regions.