Abstract: We report a detailed study of the magnetic properties of CeCo0.85Fe0.15Si under high magnetic
fields (up to 16 Tesla) measuring different physical properties such as specific heat, magnetization,
electrical resistivity, thermal expansion and magnetostriction. CeCo0.85Fe0.15Si becomes
antiferromagnetic at TN 6.7 K. However, a broad tail (onset at TX 13 K) in the specific heat
precedes that second order transition. This tail is also observed in the temperature derivative of
the resistivity. However, it is particularly noticeable in the thermal expansion coefficient where it
takes the form of a large bump centered at TX. A high magnetic field practically washes out that tail
in the resistivity. But surprisingly, the bump in the thermal expansion coefficient becomes a well
pronounced peak fully split from the magnetic transition at TN. Concurrently, the magnetoresistance
also switches from negative to positive above TN. The magnetostriction is considerable and
irreversible at low temperature ( (16T)4×10− L
L
4 at 2 K) when the magnetic interactions
dominate. A broad jump in the field dependence of the magnetostriction observed at low T may be
the signature of a weak ongoing metamagnetic transition. Taking altogether the results indicate the
importance of the lattice effects on the development of the magnetic order in these alloys.

Abstract: The linear temperature dependence of the electrical resistivity has been taken to be one of the characteristic features of the ceramic superconductors. Measurements of the electrical resistance of the LaSrCuO system in a wide temperature range show that the previous statement is only an approximation valid for some values of the Sr concentration.

Abstract: Critical current versus temperature measurements were carried out in ceramic YBa2Cu3O7 samples. The samples were all prepared using the same sintering procedure, but starting from powders obtained by different wet and dry methods. All samples showed a linear Jc vs. T behaviour, typical of Josephson weak-link coupling, with a slope that depends on the preparation method. Using the Ambegaokar-Baratoff relation for Jc, the difference in slopes can be attributed to a change in the characteristic value of the junction resistance. This value turns out to be clearly correlated with the resistivity in the normal state.

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: We have grown a-axis oriented EuBa2Cu3O7 thin films on SrTiO3 (001) substrates using a magnetron sputtering technique. In these films the CuO2 planes are aligned parallel to the substrates. The film microstructure shows microdomains. The microdomains are grains with a 90