Perovskite-carbon composites synthesized through in situ autocombustion for the oxygen reduction reaction: the carbon effect

International audienc

Epitaxial growth of gamma-CoV2O6 thin films: Structure, morphology, and magnetic properties:

We report on the epitaxial growth of 100 nm thick triclinic gamma-CoV2O6 thin films deposited by pulsed laser deposition on TiO2(100) substrate. The layers were grown in narrow experimental conditions, at 600 degrees C and 0.1 millibar oxygen pressure. X-ray diffraction and transmission electron microscopy evidenced the presence of two variants and the following epitaxial relation between the layers and the substrate: [001] TiO2(100) vertical bar vertical bar [0 +/- 10]gamma-CoV2O6(100). Besides the magnetization steps expected in gamma-CoV2O6, low temperature magnetic measurements performed along different crystalline axes show the existence of a strong anisotropy compatible with that expected from a one dimensional system, with the easy magnetization axis lying along the b direction (i.e., the Co chains). (C) 2013 AIP Publishing LLC

High Exchange Bias in Fe 3−δ O 4 @CoO Core Shell Nanoparticles Synthesized by a One-Pot Seed-Mediated Growth Method

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Correlations between structural, electronic transport, and magnetic properties of Co2FeAl0.5Si0.5 Heusler alloy epitaxial thin films

The structural and chemical order are the most important parameters governing the physical properties of the Heusler compounds. Here, we give a comprehensive overview of the correlations between structural and chemical order, electronic transport (longitudinal and transverse) and magnetic (static and dynamic) properties of Co2FeAl0.5Si0.5 Heusler alloy epitaxial thin films grown onMgO(001) single-crystal substrates. X-ray diffraction measurements indicated that depending on the annealing temperature the films show B2 or L2(1) chemical ordering. Longitudinal magnetoresistivity experiments revealed that for the best L2(1) ordered film, at temperatures bellow 125 K, the magnon assisted electronic scattering is quenched indicating the appearance of half-metallicity. The presence of quantum correction in resistivity, whose strength is dependent on the structural ordering, was evidenced at low temperatures. Anomalous Hall experiments indicated that the intrinsic band structure contribution has an opposite sign and that is dominant over the extrinsic skew scattering mechanism. The presence of a small uniaxial magnetic anisotropy contribution superimposed on a larger biaxial one was evidenced via ferromagnetic resonance microstrip line measurements. The biaxial term is well correlated with chemical ordering, having a minimum value for the optimum L2(1) ordered film. The damping parameter was evaluated from ferromagnetic resonance linewidth measurements, and a coefficient as low as 1.9 x 10(-3) was found for the L2(1) phase

High-temperature ferromagnetism in Co-doped CeO2 synthesized by the coprecipitation technique

The aim of the present study is to check the influence of annealing under vacuum and a mixture of N-2-H-2 atmosphere on the magnetic properties of polycrystalline Co-doped CeO2 diluted magnetic oxides (DMOs) with Co concentrations of 5 at% synthesized using the coprecipitation technique. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) showed for all samples the expected CeO2 cubic fluorite-type structure and that Co ions are uniformly distributed inside the samples. Room-temperature Raman and photoluminescence (PL) spectroscopies indicate an increase in the concentration of oxygen vacancies upon Co doping and further annealing. Field dependent magnetization measurements revealed a paramagnetic behavior for as-prepared Co-doped CeO2, while a ferromagnetic behavior appears when the same samples are annealed under vacuum or N-2-H-2 atmosphere. Temperature dependent magnetization measurements suggest that the observed ferromagnetism is due to the presence of metallic Co clusters with nanometric size and broad size distribution. These results are supported by electron paramagnetic resonance studies

Epitaxy of Si nanocrystals by molecular beam epitaxy on a crystalline insulator LaAlO3(001)

We have studied the Si initial growth mechanisms on LaAlO3(0 0 1), a crystalline oxide with a high dielectric constant (high-kappa material). The clean LaAlO3(0 0 1) substrate exhibits a c(2 x 2) reconstruction that can be attributed to surface O vacancies. Si deposit by molecular beam epitaxy was studied as a function of both deposition temperature and thickness. Epitaxy was obtained only above 550 degrees C. In this case, a Volmer-Weber mode is observed. The associated nanodots are relaxed and formed by pure Si as ascertained by the Si-2s XPS peak, which remains for 1 and 10 ML at the binding energy corresponding to Si-Si bonds. Moreover the islands have an abrupt interface with the LaAlO3(0 0 1) substrate without the formation of silicate or silica. A unique epitaxial relationship between LaAlO3 and the crystallized Si islands is pointed out by RHEED and confirmed by HRTEM, where the Si(0 0 1) planes are parallel to the LaAlO3(0 0 1) ones, but rotated by 45 degrees in the [0 0 1] direction. This orientation leads to mismatch and strain minimization of the Si film. (C) 2010 Elsevier B.V. All rights reserved

Structural, optical and electrical properties of Zn-doped SnO2 nanoparticles synthesized by the co-precipitation technique

Nanometric size Zn-doped SnO2 particles with Zn concentration varying from 1 to 6 % were prepared using the co-precipitation method. X-ray diffraction patterns show for all samples a typical rutile-type tetragonal structure of SnO2 without any additional peaks from spurious phases. These results together with transmission electron microscopy analyses have shown that the size of the nanoparticles decreases with Zn doping down to 4 nm. According to UV-visible absorption measurements this decrease of particle size is accompanied by a decrease of the band gap value from 3.34 eV for SnO2 down to 3.28 eV for 6 % Zn doping. The electrical conductivity of the system has been investigated between 473 and 718 K, in the 200 Hz-5 MHz frequency range, by means of impedance spectroscopy. The temperature dependence of the bulk conductivity was found to obey the Arrhenius law with activation energies of 0.74 eV for SnO2 and 0.69 eV for 6 % Zn doping

Correlation of structural properties with energy transfer of Eu-doped ZnO thin films prepared by sol-gel process and magnetron reactive sputtering

We investigated the structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique and magnetron reactive sputtering on Si (100) substrate. The films elaborated by sol-gel process are polycrystalline while the films made by sputtering show a strongly textured growth along the c-axis. X-ray diffraction patterns and transmission electron microscopy analysis show that all samples are free of spurious phases. The presence of Eu2+ and Eu3+ into the ZnO matrix has been confirmed by x-ray photoemission spectroscopy. This means that a small fraction of Europium substitutes Zn2+ as Eu2+ into the ZnO matrix; the rest of Eu being in the trivalent state. This is probably due to the formation of Eu2O3 oxide at the surface of ZnO particles. This is at the origin of the strong photoluminescence band observed at 2 eV, which is characteristic of the 5D0→7F2 Eu3+ transition. In addition the photoluminescence excitonic spectra showed efficient energy transfer from the ZnO matrix to the Eu3+ ion, which is qualitatively similar for both films although the sputtered films have a better structural quality compared to the sol-gel process grown films

Tuning of Synthesis Conditions by Thermal Decomposition toward Core–Shell Co x Fe 1– x O@Co y Fe 3– y O 4 and CoFe 2 O 4 Nanoparticles with Spherical and Cubic Shapes

International audienc