T. Toliński

The mixed-valence state of Ce in the hexagonal CeNi4B compound

Measurements of the magnetic susceptibility χ, x-ray photoemission spectra (XPS), electrical resistivity ρ and electronic structure calculations for CeNi4B are reported. In the paramagnetic region, CeNi4B follows the Curie–Weiss law with µeff = 0.52µB/fu and θ = −10.7 K. The effective magnetic moment is lower than the free Ce3+-ion value. The Ce(3d) XPS spectra have confirmed the mixed-valence state of Ce ions in CeNi4B. The f occupancy, nf, and the coupling Δ between the f level and the conduction states were derived to be about 0.83 and 85 meV, respectively. Both susceptibility data and XPS spectra show that Ce ions in CeNi4B are in the intermediate-valence state. At low temperatures (below 12 K), the magnetic contribution to the electrical resistivity reveals a logarithmic slope characteristic of Kondo-like systems.

Magnetic characteristics of RNi4B compounds (R=Y, Pr, Sm, Tb, Ho and Er)

The magnetic properties of RNi4B compounds with R=Y, Pr, Sm, Tb, Ho and Er have been studied. These compounds crystallize in a hexagonal structure with the P6/mmm space group. YNi4B shows superconducting behavior below ∼12 K, while PrNi4B is paramagnetic but contains a contribution of a ferromagnetic impurity phase. For compounds with R=Sm, Tb, Ho and Er transitions to magnetically ordered state are visible at 38, 21, 6 and 12 K, respectively. A large hysteresis loop is observed for the SmNi4B compound with a coercive field HC>7.0 T, whereas the RNi4B compounds of the other rare earths are characterized by an HC lower than 0.06 T at 5 K.

Electronic and magnetic properties of heavy fermion CeCu4Al

The studies of the magnetic susceptibility, specific heat, electrical resistivity, x-ray photoemission spectra (XPS) and the band structure calculations for CeCu4Al are reported. CeCu4Al is paramagnetic and follows the Curie?Weiss law with ?eff = 2.53??B/f.u. and ?p = ?10?K. The experimental value of ?eff is close to the calculated one for a free Ce3+ ion (2.54??B), thus indicating the presence of well-localized magnetic moments carried by the stable Ce3+ ions. Below the Fermi energy the total density of states contains mainly the d states of Cu atoms, which hybridize with the Ce f electronic states. The analysis of the Ce 3d and 4d XPS spectra indicates the localized character of the Ce f states. The determined electronic specific heat coefficient ? = 210?mJ?K?2?mol?1 confirms the heavy fermion character of the CeCu4Al compounds.

Electronic Structure of GdNi4B Compound

The GdNi 4 B compound is studied both experimentally and theoretically by X-ray photoemission spectroscopy and self-consistent tight binding linear muffin-tin orbital calculations, respectively. The density of states at the Fermi level and the magnetic moments are obtained including the influence of various atomic positions in the unit cell. The calculated magnetic moment of Ni atoms is antiparallel to the magnetic moment of Gd and depends on the local environment.

Specific heat in CeNi4Cu and YbNi4Cu

The temperature dependence of specific heat for the compounds CeNi4Cu and YbNi4Cu is analysed. These studies are supported by magnetic susceptibility and x-ray photoemission spectroscopy measurements. The scheme of the energy levels created by the splitting due to the crystal electric field is determined from the Schottky contribution to the specific heat. Anomalies observed at low temperatures are discussed in the framework of heavy-fermion/Kondo physics. It is found that an external magnetic field has a strong influence on the low temperature part of the specific heat.

Electronic structure of doped LaMnO3 perovskite studied by x-ray photoemission spectroscopy

The electronic structure of La2/3Sr1/6Pb1/6MnO3 has been studied by x-ray photoemission spectroscopy (XPS). The valence band spectrum is compared with ab initio electronic structure calculations using a linearized muffin-tin orbital (LMTO) method. The XPS measurements and the theoretical band structure calculations for La1/2Sr1/4Pb1/4MnO3 show that the electronic structure consists mainly of Mn(3d) and O(2p) states. In addition, the Mn(3d) and O(2p) states are hybridized over the whole valence band. States of 3d character localized on Mn sites predominate near the top of the valence band. It was found that the doping, both with the Pb and the Sr ions, increases the spin polarization by up to 48%.

Valence fluctuations in YbNiAl4 compound

Measurements of the magnetic susceptibility, electrical resistivity, and heat capacity are reported for the polycrystalline YbNiAl4 intermetallic compound. χ(T) has been measured up to 1000 K and its behavior is typical of a compound with the valence fluctuation between Yb3+ and Yb2+. This is especially evident from a broad maximum observed at 400 K and interpreted in frames of the interconfiguration fluctuation model. The Sommerfeld coefficient derived from the heat capacity measurements takes a small value of γ=16 mJ mol−1 K−2. The low temperature resistivity follows the AT2 dependence characteristic of a Fermi liquid.

Magnetostructural transformations in Ni51Mn36Sn13 Heusler alloy thin films

In this paper we report structural, magnetic and transport properties of strongly textured Ni51Mn36Sn13 thin films. The off-stoichiometric Heusler alloy films with 200 nm thickness were sputter-deposited on a MgO(100) substrate at 500 K and after annealed at 1000 K in UHV conditions. The textured growth was confirmed by x-ray diffraction in Bragg-Brentano geometry. The temperature dependence of the magnetic properties was measured by VSM and FMR methods. The electron transport measurements were carried out in function of temperature in 0 Oe and 50 kOe fields. All measurements corroborate the existence of the martensitic transformation in the film. Furthermore, transport measurements reveal an influence of the magnetic field on the transition temperature.

Magnetic and transport properties of Tm2Co7B3 compound

Magnetic and transport properties of Tm2Co7B3 compound have been studied. This compound crystallizes in the hexagonal Ce2Co7B3 type structure. The coercivity (Hc) of the compound was determined from hysteresis measurements in fields up to 4 T. The temperature dependence of coercivity has been explained by a thermally activated process of domain wall motion. The resistivity at low temperatures shows a T2 dependence. At higher temperatures the resistivity is not a linear function of temperature, which indicates an electron-phonon interaction in the presence of a small s-d scattering.

Structural effects of grinding on La0.7Sr0.3MnO3 ceramic studied by neutron diffraction

Abstract The bulk and powdered La0.7Sr0.3MnO3 ceramic sample was investigated by neutron diffraction in the temperature range from 80 to 280 K and in magnetic field up to 4.5 T. The crystallographic and magnetic structures were analyzed by the Rietveld method. An increased contribution of the orthorhombic Pbnm phase was observed after powdering the bulk ceramic sample with rhombohedral structure described by the R3c space group. The appearance of the orthorhombic part (20–30%) was explained by Sr or/and O escape out of the grain surface. The refined magnetic moment, μ=3.7 μB, was consistent with the theoretical value calculated from the hole doping level. The temperature dependence of the unit-cell parameters of the dominating rhombohedral phase was also determined.