Dario Niebieskikwiat

Fe and Mo Valences in Sr2FeMoO6

Abstract The valences of Fe and Mo in Sr 2 FeMoO 6 are investigated by means of X-ray absorption and photoemission spectroscopies. We find that the d occupations are similar to those of Fe in Fe 2 O 3 and Mo in MoO 3 . Considering the covalency, however, we argue that the ground state is closer to a Fe +3 (3 d 5 )–Mo +5 (4 d 1 ) configuration than to a Fe +2 (3 d 6 )–Mo +6 (4 d 0 ) configuration.

Phase separation region in the phase diagram of polycrystalline Pr0.65Ca0.35−xSrxMnO3

Abstract We have performed measurements of thermoelectric power, electrical resistivity and DC magnetization in polycrystalline samples of Pr 0.65 Ca 0.35− x Sr x MnO 3 with x =0, 0.02, 0.05, 0.10 and 0.20. The system presents an evolution from a charge-ordered manganite at x =0, with an insulating-like resistivity and low magnetization values, towards a ferromagnetic (FM) metallic state for x =0.20. We show that in the intermediate region a strong competition between the FM double-exchange and the localized charge-ordering occurs, inducing the phase segregation of the two competing states in a wide temperature range. We estimate the temperature ( T ) evolution of the FM phase fraction of the x =0.10 sample and construct a complete T − x phase diagram.

Enhancement of the low field magnetoresistance by grain boundary modification in Sr2FeMoO6+δ

Abstract We study the magnetic and electric properties of polycrystalline Sr 2 FeMoO 6+ δ with controlled oxygen content, for nominal values δ =0 and 0.04. While the magnetization and lattice parameters are the same in both samples, the resistivity and the magnetoresistance are greatly enhanced in the δ =0.04 sample. This behavior is related to the formation of an impurity (insulating) phase at the grain boundaries, thus reinforcing the intergrain tunneling barrier.

Electronic structure of Sr2FeMoO6

Abstract We have used electron spectroscopies to investigate the electronic structure of the double perovskite Sr2FeMoO6. The valence-band photoemission spectra present a well-defined cut-off at the Fermi level, indicative of the metallic character of the material. The O 1s X-ray absorption spectrum presents three peaks, which are in good correspondence with the main structures in the unoccupied density-of-states of DF-LDA calculations. The electron energy-loss spectra present two structures which are also interpreted in terms of transitions between the bands obtained in the DF-LDA calculations.

Hole-doping dependence of percolative phase separation in Pr 0.5 − δ Ca 0 . 2 + δ Sr 0.3 MnO 3 around half doping

We address the problem of the percolative phase separation in polycrystalline samples of

Nonlinear behavior of V-I curves at low temperatures in nanoparticles of La2/3B1/3MnO3 with B = Ca, Sr

{\mathrm{Pr}}_{0.5\ensuremath{-}\ensuremath{\delta}}{\mathrm{Ca}}_{0.2+\ensuremath{\delta}}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}

Spin-polarized tunneling in nanostructured La2/3Sr1/3MnO3

for

Asymmetric phase diagram and phase separation in Pr0.5−δCa0.2+δSr0.3MnO3 (−0.04⩽δ⩽0.04)

\ensuremath{-}0.04l~\ensuremath{\delta}l~0.04

Oxygen-induced grain boundary effects on magnetotransport properties of Sr 2 FeMoO 6 + δ

(hole doping n between

High-temperature properties of theSr2FeMoO6double perovskite: Electrical resistivity, magnetic susceptibility, and ESR

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