2,329 research outputs found

    Evidences for Tsallis non-extensivity on CMR manganites

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    We found, from the analysis of MM vs. TT curves of some manganese oxides (manganites), that these systems do not follow the traditional Maxwell-Boltzmann statistics, but the Tsallis statistics, within the \QTR{em}{normalized} formalism. Curves were calculated within the mean field approximation, for various ferromagnetic samples and the results were compared to measurements of our own and to various other authors published data, chosen at random from the literature. The agreement between the experimental data and calculated MqM_{q} vs. TT^{\ast} curve, where TT^{\ast} is an effective temperature, is excellent for all the compounds. The entropic parameter, qq, correlates in a simple way with the experimental value of TcT_{c}, irrespect the chemical composition of the compounds, heat treatment or other details on sample preparation. Examples include q<1q<1 (superextensivity), q=1q=1 (extensivity) and q>1q>1 (subextensivity) cases.Comment: 12 pages, 3 figure

    Interplay of superexchange and orbital degeneracy in Cr-doped LaMnO3

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    We report on structural, magnetic and Electron Spin Resonance (ESR) investigations in the manganite system LaMn_{1-x}Cr_{x}O_{3} (x<=0.5). Upon Cr-doping we observe a reduction of the Jahn-Teller distortion yielding less distorted orthorhombic structures. A transition from the Jahn-Teller distorted O' to the pseudocubic O phase occurs between 0.3<x<0.4. A clear connection between this transition and the doping dependence of the magnetic and ESR properties has been observed. The effective moments determined by ESR seem reduced with respect to the spin-only value of both Mn^{3+} and Cr^{3+} ions

    Structural, magnetic and electrical properties of single crystalline La_(1-x)Sr_xMnO_3 for 0.4 < x < 0.85

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    We report on structural, magnetic and electrical properties of Sr-doped LaMnO_3 single crystals for doping levels 0.4 < x < 0.85. The complex structural and magnetic phase diagram can only be explained assuming significant contributions from the orbital degrees of freedom. Close to x = 0.6 a ferromagnetic metal is followed by an antiferromagnetic metallic phase below 200 K. This antiferromagnetic metallic phase exists in a monoclinic crystallographic structure. Following theoretical predictions this metallic antiferromagnet is expected to reveal an (x^2-y^2)-type orbital order. For higher Sr concentrations an antiferromagnetic insulator is established below room temperature.Comment: 8 pages, 7 figure

    Crystal Field and Dzyaloshinsky-Moriya Interaction in orbitally ordered La_{0.95}Sr_{0.05}MnO_3: An ESR Study

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    We present a comprehensive analysis of Dzyaloshinsky-Moriya interaction and crystal-field parameters using the angular dependence of the paramagnetic resonance shift and linewidth in single crystals of La_{0.95}Sr_{0.05}MnO_3 within the orthorhombic Jahn-Teller distorted phase. The Dzyaloshinsky-Moriya interaction (~ 1K) results from the tilting of the MnO_6 octahedra against each other. The crystal-field parameters D and E are found to be of comparable magnitude (~ 1K) with D ~= -E. This indicates a strong mixing of the |3z^2-r^2> and |x^2-y^2> states for the real orbital configuration.Comment: 12 pages, 6 figure

    A Detailed XRD and FTIR Analysis of Bi2O3 Doped ZnO-SnO2 Ceramics

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    Poster presented at the 2nd International Congress on Ceramics, Verona, Italy, June 29 - July 4, 200

    Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces

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    We investigate the transport properties of a ferromagnet-superconductor interface within the framework of a modified three-dimensional Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge inhomogeneity forms via two unique transport mechanisms, namely, evanescent Andreev reflection and evanescent quasiparticle transmission. Furthermore, we take into account the influence of charge inhomogeneity on the interfacial barrier potential and calculate the conductance as a function of bias voltage. Point-contact Andreev reflection (PCAR) spectra often show dip structures, large zero-bias conductance enhancement, and additional zero-bias conductance peak. Our results indicate that transport-induced charge inhomogeneity could be a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure

    Formalising the Continuous/Discrete Modeling Step

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    Formally capturing the transition from a continuous model to a discrete model is investigated using model based refinement techniques. A very simple model for stopping (eg. of a train) is developed in both the continuous and discrete domains. The difference between the two is quantified using generic results from ODE theory, and these estimates can be compared with the exact solutions. Such results do not fit well into a conventional model based refinement framework; however they can be accommodated into a model based retrenchment. The retrenchment is described, and the way it can interface to refinement development on both the continuous and discrete sides is outlined. The approach is compared to what can be achieved using hybrid systems techniques.Comment: In Proceedings Refine 2011, arXiv:1106.348

    The Orbital Order Parameter in La0.95Sr0.05MnO3 probed by Electron Spin Resonance

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    The temperature dependence of the electron-spin resonance linewidth in La0.95Sr0.05MnO3 has been determined and analyzed in the paramagnetic regime across the orbital ordering transition. From the temperature dependence and the anisotropy of linewidth and gg-value the orbital order can be unambiguously determined via the mixing angle of the wave functions of the ege_{\rm g}-doublet. The linewidth shows a similar evolution with temperature as resonant x-ray scattering results
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