17,755 research outputs found

    Lattice structure and magnetization of LaCoO3 thin films

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    We investigate the structure and magnetic properties of thin films of the LaCoO3_{3} compound. Thin films are deposited by pulsed laser deposition on various substrates in order to tune the strain from compressive to tensile. Single-phase (001) oriented LaCoO3_{3} layers were grown on all substrates despite large misfits. The tetragonal distortion of the films covers a wide range from -2% to 2.8%. Our LaCoO3_{3} films are ferromagnetic with Curie temperature around 85 K, contrary to the bulk. The total magnetic moment is below 1μB1\mu_{B}/Co3+^{3+}, a value relatively small for an exited spin-state of the Co3+^{3+} ions, but comparable to values reported in literature. A correlation of strain states and magnetic moment of Co3+^{3+} ions in LaCoO3_{3} thin films is observed.Comment: submitted tu European Phys. J.

    Strain-induced insulator state in La_0.7Sr_0.3CoO_3

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    We report on the observation of a strain-induced insulator state in ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to enhance the resistivity by several orders of magnitude. Reversible strain of 0.15% applied using a piezoelectric substrate triggers huge resistance modulations, including a change by a factor of 10 in the paramagnetic regime at 300 K. However, below the ferromagnetic ordering temperature, the magnetization data indicate weak dependence on strain for the spin state of the Co ions. We interpret the changes observed in the transport properties in terms of a strain-induced splitting of the Co e_g levels and reduced double exchange, combined with a percolation-type conduction in an electronic cluster state

    A 'p-n' diode with hole and electron-doped lanthanum manganite

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    The hole-doped manganite La0.7Ca0.3MnO3 and the electron-doped manganite La0.7Ce0.3MnO3 undergo an insulator to metal transition at around 250 K, above which both behave as a polaronic semiconductor. We have successfully fabricated an epitaxial trilayer (La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3), where SrTiO3 is an insulator. At room temperature, i.e. in the semiconducting regime, it exhibits asymmetric current-voltage (I-V) characteristics akin to a p-n diode. The observed asymmetry in the I-V characteristics disappears at low temperatures where both the manganite layers are metallic. To the best of our knowledge, this is the first report of such a p-n diode, using the polaronic semiconducting regime of doped manganites.Comment: PostScript text and 2 figures, to be published in Appl. Phys. Lett

    The role of carbon for superconductivity in MgCx_{x}Ni3_{3} from specific heat

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    The influence of carbon deficiency on superconductivity of MgCNi3_{3} is investigated by specific heat measurements in the normal and superconducting state. In order to perform a detailed analysis of the normal state specific heat, a computer code is developed which allows for an instantaneous estimate of the main features of the lattice dynamics. By analyzing the evolution of the lattice vibrations within the series and simultaneously considering the visible mass enhancement, the loss in the electron-phonon coupling can be attributed to significant changes of the prominent Ni vibrations. The present data well supports the recently established picture of strong electron-phonon coupling and ferromagnetic spin fluctuations in this compound.Comment: 4 pages, latex, corrections to the text, one reference added, one figure correcte

    Reversible strain effect on the magnetization of LaCoO3 films

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    The magnetization of ferromagnetic LaCoO3 films grown epitaxially on piezoelectric substrates has been found to systematically decrease with the reduction of tensile strain. The magnetization change induced by the reversible strain variation reveals an increase of the Co magnetic moment with tensile strain. The biaxial strain dependence of the Curie temperature is estimated to be below 4K/% in the as-grown tensile strain state of our films. This is in agreement with results from statically strained films on various substrates

    Weak inter-band coupling in Mg10^{10}B2_{2}: a specific heat analysis

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    The superconducting state of Mg10^{10}B2_{2} is investigated by specific heat measurements in detail. The specific heat in the normal state is analyzed using a recently developed computer code. This allows for an extraction of the electronic specific heat in the superconducting state with high accuracy and a fair determination of the main lattice features. One of the two investigated samples shows a hump in the specific heat at low temperatures within the superconducting state, accompanied by an unusual low value of the small gap, Δπ(0)=1.32meV\Delta_{\pi}(0)=1.32 meV, pointing to a very weak inter-band coupling. This sample allows for a detailed analysis of the contribution from the π\pi-band to the electronic specific heat in the superconducting state. Therefore the usual analysis method is modified, to include the individual conservation of entropy of both bands. From analyzing the deviation function D(t)D(t) of MgB2_{2}, the theoretically predicted weak inter-band coupling scenario is confirmed.Comment: major revision
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