Andrzej Slebarski

Kondo insulating behaviour in the filled skutterudite compound CeOs4Sb12

The filled skutterudite CeOs4Sb12 and its nonmagnetic analogue LaOs4Sb12 have been synthesized in single-crystal form using the molten-metal-flux growth technique with Sb flux. Electrical resistivity measurements on CeOs4Sb12 indicate that it is a Kondo insulator with an energy gap of ΔE/kB~10 K. Lattice parameter and magnetic susceptibility measurements suggest that the Ce ions are trivalent in CeOs4Sb12. Specific heat and magnetization measurements reveal an enhanced value of the electronic specific heat coefficient γ~92 mJ mol-1 K-2 and Pauli susceptibility, reminiscent of a moderately heavy-fermion material.

Electronic and magnetic investigation of the filled skutterudite compound CeRu4Sb12

We synthesized the filled skutterudite CeRu4Sb12 in single-crystal form using a molten-metal-flux technique with Sb flux. The specific heat and magnetic susceptibility of CeRu4Sb12 are well described by a logarithmic divergence or a power law in temperature indicating non-Fermi-liquid behaviour at low temperatures. The electrical resistivity is sample dependent with some specimens exhibiting non-Fermi-liquid behaviour below T~5 K in which ρ∝Tn with n~1.4. The application of magnetic fields up to H = 80 kOe does not significantly change the non-Fermi-liquid ground state.

Magnetic splitting in x-ray photoelectron spectroscopy Cr L spectra of Fe2CrAl, Co2CrAl and Cu2CrAl

We have investigated various Cr-based Heusler alloys using core-level x-ray photoelectron spectroscopy (XPS). Of special interest are the 2p XPS lines, which always exhibit magnetic splitting in the case of the existence of a well-defined local magnetic moment at the transition metal site. The Cr 2p XP spectra, however, do not exhibit this exchange splitting for the nonmagnetic Cu2CrAl sample and for Fe2CrAl or Co2CrAl alloys with a magnetic moment at the Cr sites of about 1.6 μB. This behaviour is discussed here.

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%.

Structural properties and electronic structure of some ternary d-electron and f-electron intermetallics

We report on structural measurements on and electronic structure investigations of the alloyed compounds ZrNiSn, TiNiSn, CeNiSn and CeRhSb. We present measurements of lattice parameters as a function of temperature and analysis of a (T ) and its relation to T , being the magnetic susceptibility. We observed a linear dependence of a (T ) versus T for Zr, Ti and Ce alloys (for orthorhombic Ce alloys, the lattice parameters a , b and c scale linearly with T ). The x-ray photoelectron and ultraviolet photoemission spectra are further compared to the density of states, obtained from band-structure calculations.

From Kondo semimetal to spin-glass behaviour in doped CeNi1−δSn1+δ−x Sb x system

We investigate the properties of the off-stoichiometric CeNi1−δSn1+δ−x Sb x systems with δ ≈ 0.06 and 0 < x ≤ 0.22. Such a semimetallic CeNi1−δSn1+δ−x Sb x system is shown to transform into a Kondo semiconductor upon the substitution of about 2% of Sb for Sn. The effects of Sb doping on the low-temperature properties of CeNiSn were studied by means of electrical resistivity, magnetic susceptibility and specific heat. We interpret the ground state properties of the series of CeNi1−δSn1+δ−x Sb x compounds as resulting from the change in carrier number acting together with the hybridisation between the 4f electrons and the conduction electrons. For the Kondo semiconductor state we observe the scaling law χρ = const. of the susceptibility χ and the resistivity ρ, which is regarded as the basic feature for this class of materials, as was reported earlier. The magnetic properties of the system gradually evolve from the Kondo semimetallic state to the spin-glass behaviour when the Sb doping increases.