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International audience; We studied the electronic and magnetotransport properties of Sr1-xLaxRu1-xCoxO3 epitaxial thin films (0 ≤ x ≤ 0.30) grown on atomically flat SrTiO3 (001) substrates. The epitaxial strain from the SrTiO3 substrate would give compressive strain on Sr1-xLaxRu1-xCoxO3 when the film has the same amount of charge transfer as that observed in the bulk sample. If the epitaxial strain applied by the SrTiO3 substrate overrides the charge transfer, it can block half the amount of charge transfer. However, the observed unit cell volume and X-ray photoelectron spectroscopy data clearly reveal that the amount of charge transfer in our epitaxial thin film is approximately the same as that observed in the previously reported bulk samples. The saturation magnetization decreased for all Sr1-xLaxRu1-xCoxO3 thin films, with an increase in the antiferromagnetic behavior. The zero-field resistivity value of all the compositions increased systematically, with a higher resistivity observed at x = 0.30 (ρ(T = 10 K) 450 mΩ cm). A large negative magnetoresistance of up to ∼24.8% was also observed at x = 0.30 (H = 9 T, T = 10 K). We tried to explain our data in terms of super exchange interaction added to existing double exchange interaction between Ru–Co networks.

Oxygen stoichiometry is one of the most important elements in determining the physical properties of transition metal oxides (TMOs). A small fractional change in the oxygen content, resulting in the variation of valence state of the transition metal, can drastically modify the materials functionalities. In particular, TMOs with mixed valences have attracted attention for many energy applications. Previous studies also showed that the ability to control the number of d-band electron populations and detailed spin configurations is critical for improved catalytic performance of TMOs. In this context, SrCoO$_{x}$ (2.5 < x < 3.0) is an ideal class of materials due to the existence of two structurally distinct topotatic phases, i.e. the brownmillerite SrCoO$_{2.5}$(BM-SCO) and the perovskite SrCoO$_{3}$. Especially, BM-SCO has atomically-ordered one-dimensional vacancy channels, which can accommodate additional oxygen. Moreover, SrCoO$_{x}$ exhibits a wide spectrum of physical properties depending on the oxygen stoichiometry. Since SrCoOx has only a single knob to control the Co valence state without cation doping, it is an attractive material for studying the valence state dependent physical properties. However, so far, the growth of high quality single crystalline materials has not been much studied due to difficulty in controlling the right oxidation state. In this work, we report on the epitaxial growth of BM-SCO single crystalline films on SrTiO3 by pulsed laser epitaxy. In order to examine the topotactic phase transformation to the perovskite SrCoO$_{3-��}$, some of samples were subsequently in-situ annealed at various oxygen pressure P(O$_{2}$). We found that post-annealing in high P(O$_{2}$) (> several hundreds of Torr) could fill some of oxygen vacancies accompanying systematic evolution in electronic, magnetic, and thermoelectric properties.

We investigated the temperature dependence of the upper critical field [$H_{c2}(T)$] of fluorine-free SmFeAsO$_{0.85}$ and fluorine-doped SmFeAsO$_{0.8}$F$_{0.2}$ single crystals by measuring the resistive transition in low static magnetic fields and in pulsed fields up to 60 T. Both crystals show that $H_{c2}(T)$'s along the c axis [$H_{c2}^c(T)$] and in an $ab$-planar direction [$H_{c2}^{ab}(T)$] exhibit a linear and a sublinear increase, respectively, with decreasing temperature below the superconducting transition. $H_{c2}(T)$'s in both directions deviate from the conventional one-gap Werthamer-Helfand-Hohenberg theoretical prediction at low temperatures. A two-gap nature and the paramagnetic pair-breaking effect are shown to be responsible for the temperature-dependent behavior of $H_{c2}^c$ and $H_{c2}^{ab}$, respectively., 21 pages, 8 figures

We report fluctuation magnetoconductance in a MgB2 superconductor prepared under a high pressure of 3 GPa. This excess magnetoconductance, $\Delta\sigma(H)$, follows the three-dimensional scaling function for the critical fluctuations proposed by Ullah and Dorsey. This feature is inferred to originate from the isotropic nature of the MgB2 compound., Comment: 3 pages, 2 figures