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In the paper we present and discuss magnetic properties of the Gd(Ni1–x Fex)3 crystalline compounds and their ball‐milled powders in a context of the magnetocaloric effect (MCE). Moreover, based on the obtained results, powders and composites with non‐magnetic (Cu) and magnetic (Fe) additions were prepared. Magnetic quantities such as the Curie temperature, the saturation magnetization and the MCE (as a magnetic entropy change) were determined for all examined samples. In the case of the bulk crystalline compounds a partial substitution of Ni by Fe atoms causes a decrease of the saturation magnetization as well as the MCE and an increase of the Curie temperature. Samples with x ranging from 0.1 to 0.15 show the best potential for room‐temperature refrigeration. Pulverization of the tested compounds leads to formation of flake‐like grains with thickness less than 1 μm. Such grinding causes a decrease of the Curie temperature (by about 10 K) as well as the MCE (by about 50%) in a comparison with the crystalline samples. In the case of the composite with magnetic addition an enhancement of the MCE was observed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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The magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and thermal conductivity measurements in a wide temperature range have been performed on UCoGa 5 single crystals. On the basis of the susceptibility maximum at 650 K and the phonon part of the thermal conductivity, a mixed-valence state of uranium in this compound has been postulated. On the other hand, a normal positive behavior of magnetoresistivity rules out the possibility of spin fluctuation as a mechanism driving the susceptibility through the maximum. In turn, the thermopower results may support both kinds of many-body behaviors. The electronic structure has also been studied by combining x-ray photoemission spectroscopy results with those obtained in the band structure calculations. In the latter the tight-binding linear muffin-tin orbital method in the atomic sphere approximation has been applied. A very good agreement between the experimental and calculated data has been achieved. A complex satellite structure of the core level spectra supports an idea of the presence of the valence instability in this compound. This idea is also concluded from the comparison of obtained experimental data with some similar rare earth and uranium ternary compounds.