Abstract: New double perovskites LaPbMSbO₆, where M²⁺ = Mn²⁺, Co²⁺, and Ni²⁺, were synthesized as polycrystals by an aqueous synthetic route at temperatures below 1000 ^°C. All samples are monoclinic, space group P2₁/n, as it is observed from Rietveld analysis of X-ray powder diffraction patterns. The distribution of M²⁺ and Sb⁵⁺ among the two octahedral sites have 3% of disorder for M²⁺ = Ni²⁺, whereas for M²⁺ = Mn²⁺ and Co²⁺ less disorder is found. The three samples have an antiferromagnetic transition, due to the antiferromagnetic coupling between M^{2 +} through super-superexchange paths M²⁺-O^2--Sb⁵⁺-O^2--M²⁺. Transition temperatures are low: 8, 10 and 17 K for Mn²⁺, Co²⁺, and Ni^{2 +} respectively, as a consequence of the relatively long distances between the magnetic ions M²⁺. Besides, for LaPbMnSbO₆ a small transition at 45 K was found, with ferrimagnetic characteristics, possibly as a consequence of a small disorder between Mn²⁺ and Sb⁵⁺. This disorder would give additional and shorter interaction paths: superexchange Mn²⁺-O^2--Mn²⁺.

Abstract: The synthesis, structural characterization, and magnetic properties of La3Co2SbO9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P21/n. Co2+ and Sb5+ have the maximum order allowed for the La3Co2SbO9 stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) Å, b=5.6842(2) Å, c=7.9748(2) Å and β=89.999(3)°. Magnetization measurements indicate the presence of ferromagnetic correlations with TC=55 K attributed to the exchange interactions for non-linear Co2+–O–Sb5+–O–Co2+ paths. The effective magnetic moment obtained experimentally is μexp=4.38 μB (per mol Co2+), between the theoretical one for spin only (3.87 μB) and spin-orbit value (6.63 μB), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 μB/f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration.

Abstract: Y[Fe(CN)6]·4H2O has been synthesized and characterized. The crystal structure was refined by Rietveld analysis using X-ray powder diffraction data. Y[Fe(CN)6]·4H2O crystallizes in the orthorhombic crystal system, space group Cmcm. Y3+ ion is eight-coordinated forming a bicapped distorted trigonal prism YN6O2. Fe3+ ion is six-coordinated in the form of an irregular octahedra FeC6 group and cyanide linkages between YN6O2 and FeC6 groups build an infinite polymeric array. The vibrational spectrum shows two bands corresponding to antisymmetric and symmetric stretching 12C14N in the CN stretching region. These bands are accompanied by four weak isotopic bands at lower frequency due to the presence of 13C and 15N in relative natural abundance. The HOH bending band split into three bands around 1600 cm−1 due to the presence of two kinds of water molecules in the structure. The thermal decomposition has been followed by thermogravimetric and differential thermal analysis, IR spectroscopy and powder XRD. The size and morphology of the complex and its thermal decomposition products were evaluated by scanning electron microscopy. The magnetic measurements confirm that Y[Fe(CN)6]·4H2O shows an antiferromagnetic order at low temperatures.

Abstract: Oxygen vacancies in oxides nanostructures are the origin of many intriguing phenomena. We have studied the influence of the oxygen pressure in the tunneling properties of a ferroelectric barrier, Ba0.25Sr0.75TiO3 (BSTO), grown over a ferromagnetic electrode. A phenomenological model description was used to obtain critical information about the structure and electrical properties of ultra-thin BSTO layers using conductive atomic force microscopy. The BSTO layers present good insulation properties. Reducing the oxygen content increases the conductivity of the samples. The tunneling of the current carriers is probably the main conduction mechanism for samples with higher barrier thicknesses.

Abstract: The orthorhombic CePd1-xRhx alloy exhibits a continuous evolution from a ferromagnetic ground state at x = 0 to
intermediate-valence behavior for x = 1. Here, we report on specific heat CP(T), resistivity ρ(T) and magnetization M(T)
measurements on single crystals in a Rh concentration range 0.2 < x < 0.65 exploring the ferromagnetic side of the
magnetic phase diagram. The transport and thermodynamic properties of the ferromagnetic phase have been investigated
in the temperature range from 300 K down to 0.35 K and analyzed in terms of a gap in the magnon spectrum and an
underlying Kondo contribution. Crystal electric field parameters are deduced from specific heat measurements well above
Tc- The competition between Kondo effect and ferromagnetism has been studied in dependence of the Rh concentration in
the system. Particularly, the enhanced Sommerfeld coefficient γ(x) indicates strong Kondo interactions when the Curie
temperature is reduced.