Magnetomechanical and magnetoelectric effects, magnetostriction PACS 78.30.-j -Infrared and Raman spectra PACS 63.20.-e -Phonons in crystal lattices PACS 77.22.-d -Dielectric properties of solids and liquidsAbstract. -Infrared reflectivity and time-domain terahertz transmission spectra of EuTiO3 ceramics revealed a polar optic phonon at 6 -300 K whose softening is fully responsible for the recently observed quantum paraelectric behaviour. Even if our EuTiO3 ceramics show lower permittivity than the single crystal due to a reduced density and/or small amount of secondary pyrochlore Eu2Ti2O7 phase, we confirmed the magnetic field dependence of the permittivity, also slightly smaller than in single crystal. Attempt to reveal the soft phonon dependence at 1.8 K on the magnetic field up to 13 T remained below the accuracy of our infrared reflectivity experiment.

We present a detailed study of the evolution of the electrical, galvanomagnetic, and thermodynamic properties of polycrystalline Ag x Mo 9 Se 11 compounds for 3.4 ≤ x ≤ 3.8 at low temperatures (2−350 K). In agreement with density functional theory calculations, the collected data show an overall gradual variation in the transport properties from metallic to semiconducting behavior on going from x = 3.4 to 3.8. The results evidence subtle variations in the electronic properties with the Ag content, typified by both positive and negative phonon-drag effects together with thermopower and Hall coefficient of opposite signs. Analysis of the data suggests that these features may be due to peculiarities of the dispersion of the valence bands in the vicinity of the chemical potential. A drastic influence of the Ag content on the thermal transport was evidenced by a pronounced change in the temperature dependence of the specific heat below 10 K. Nonlinearities in the C p (T 3 ) data are correlated to the concentration of Ag atoms, with an increase in x resulting in a more pronounced departure from a Debye law. The observed behavior mirrors that of ionic conductors, suggesting that Ag x Mo 9 Se 11 for x ≥ 3.6 might belong to this class of compounds.

The magnetic, electric and thermal properties of the (Ln 1−y Y y ) 0.7 Ca 0.3 CoO 3 perovskites (Ln = Pr, Nd) were investigated down to very low temperatures. The main attention was given to a peculiar metal-insulator transition, which is observed in the praseodymium based samples with y = 0.075 and 0.15 at T M −I = 64 and 132 K, respectively. The study suggests that the transition, reported originally in Pr 0.5 Ca 0.5 CoO 3 , is not due to a mere change of cobalt ions from the intermediate-to the low-spin states, but is associated also with a significant electron transfer between Pr 3+ and Co 3+ /Co 4+ sites, so that the praseodymium ions occur below T M −I in a mixed Pr 3+ /Pr 4+ valence. The presence of Pr 4+ ions in the insulating phase of the yttrium doped samples (Pr 1−y Y y ) 0.7 Ca 0.3 CoO 3 is evidenced by Schottky peak originating in Zeeman splitting of the ground state Kramers doublet. The peak is absent in pure Pr 0.7 Ca 0.3 CoO 3 in which metallic phase, based solely on non-Kramers Pr 3+ ions, is retained down to the lowest temperature.

Temperature dependences of the magnetic susceptibility, specific heat, and electrical resistivity have been measured for the Mo(3)Sb(7) compound in the 0.6-350 K range. This compound exhibits bulk superconductivity occurring at 2.25 K and follows the Kadowaki-Woods relation, A/gamma(2)=1.0 x 10(-5) microOmega x cm(K x mol/mJ)(2), as a heavy-fermion system does. We show, from experimental evidence and theoretical argument, that Mo(3)Sb(7) can be classified as a coexistent superconductor-spin fluctuation system. The McMillan equation including paramagnon effects was found to give an accurate estimation of the transition temperature.