270 research outputs found

    Role of Orbital Degeneracy in Double Exchange Systems

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    We investigate the role of orbital degeneracy in the double exchange (DE) model. In the JH→∞J_{H}\to\infty limit, an effective generalized ``Hubbard'' model incorporating orbital pseudospin degrees of freedom is derived. The model possesses an exact solution in one- and in infinite dimensions. In 1D, the metallic phase off ``half-filling'' is a Luttinger liquid with pseudospin-charge separation. Using the d=∞d=\infty solution for our effective model, we show how many experimental observations for the well-doped (x≃0.3x\simeq 0.3) three-dimensional manganites La1−xSrxMnO3La_{1-x}Sr_{x}MnO_{3} can be qualitatively explained by invoking the role of orbital degeneracy in the DE model.Comment: 8 pages, 2 figures, submitted to Phys. Rev.

    Specific heat study of single crystalline Pr0.63_{0.63} Ca0.37_{0.37} MnO3_{3} in presence of a magnetic field

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    We present the results of a study of specific heat on a single crystal of Pr0.63_{0.63}Ca0.37_{0.37}MnO3_3 performed over a temperature range 3K-300K in presence of 0 and 8T magnetic fields. An estimate of the entropy and latent heat in a magnetic field at the first order charge ordering (CO) transition is presented. The total entropy change at the CO transition which is ≈\approx 1.8 J/mol K at 0T, decreases to ∼\sim 1.5 J/mol K in presence of 8T magnetic field. Our measurements enable us to estimate the latent heat LCOL_{CO} ≈\approx 235 J/mol involved in the CO transition. Since the entropy of the ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered insulating (COI) state, a subtle change in entropy stabilises either of these two states. Our low temperature specific heat measurements reveal that the linear term is absent in 0T and surprisingly not seen even in the metallic FMM state.Comment: 8 pages (in RevTEX format), 12 figures (in postscript format) Submitted to Phys. Rev.

    Anisotropic phonon conduction and lattice distortions in CMR-type bilayer manganite (La1−z_{1-z}Prz_{z})1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7} (z=0,0.2,0.4 and 0.6) single crystals

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    We have undertaken a systematic study of thermal conductivity as a function of temperature and magnetic field of single crystals of the compound (La1−z_{1-z}Prz_{z})1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7} for zz(Pr) =0.2,0.4. and 0.6. The lattice distortion due to Pr-substitution and anisotropic thermal conductivity in bilayer manganites are discussed on the basis of different relaxation models of local lattice distortions in metal and insulating states proposed by Maderda et al. The giant magnetothermal effect is scaled as a function of magnetization and discussed on the basis of a systematic variation of the occupation of the ege_g-electron orbital states due to Pr-substitution.Comment: 7 pages, 6 figures, in press in Phys.Rev.

    Phase Transition in Perovskite Manganites with Orbital Degree of Freedom

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    Roles of orbital degree of freedom of Mn ions in phase transition as a function of temperature and hole concentration in perovskite manganites are studied. It is shown that the orbital order-disorder transition is of the first order in the wide region of hole concentration and the NeËŠ\rm \acute{e}el temperature for the anisotropic spin ordering, such as the layer-type antiferromagnetic one, is lower than the orbital ordering temperature due to the anisotropy in the orbital space. The calculated results of the temperature dependence of the spin and orbital order parameters explain a variety of the experiments observed in manganites.Comment: 10 pages, 5 figure

    Corruption and its effects on FDI:Analysing the interaction between the corruption levels of the home and host countries and its effects at the decision-making level

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    This study furthers our understanding of how corruption affects the decision-making process of allocating foreign direct investment. Drawing on the responses of 28 managers in charge of establishing operations in a highly corrupt host country, we argue that those firms based in home countries with low levels of corruption are more proactive in preparing to face corruption abroad than those based in countries with high corruption levels. This means that firms from less corrupt home countries have strategies in place to deal with high corruption abroad. This finding is based on the fact that these firms have stronger pressures to not engage in corruption from their home stakeholders. Also, these firms might not have the experience of dealing with corruption at home, which hinders their potential to deal with corruption abroad. On the other hand, those firms based in highly corrupt home countries do not have clear strategies to deal with corruption abroad. This assertion is based on the fact that these firms might have familiarity in dealing with corruption and thus, might not see it as an obstacle to operating abroad
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