Magnetic and Transport Properties of (La,Sr)MnO3_3

Magnetic and transport properties of the perovskite-type $3d$ transition-metal oxide (La,Sr)MnO$_3$ are theoretically studied using the double-exchange model in infinite dimension. Magnetoresistance properties as well as the magnetic transition temperatures are in good agreement with the experimental data.Comment: 5 pages, LaTeX, including 2 PS figures. To be published in Proc. International Symposium 'Frontiers of High Tc Superconductivity' (Oct. 1995, Morioka, Japan

Phase competition in the double-exchange model on the frustrated pyrochlore lattice

Competition between the ferromagnetic double-exchange interaction and the super-exchange antiferromagnetic interaction is theoretically studied in the presence of geometrical frustration. As increasing the super-exchange interaction, the ferromagnetic metal becomes unstable, and is taken over by a cooperative paramagnetic metal, in sharp contrast with a discontinuous transition to the antiferromagnetic insulator in the absence of frustration. In the critical region, the system exhibits a peculiar temperature-independent behavior with highly incoherent transport, suggesting a large residual entropy at low temperatures. We discuss the relevance of the results to the pressure-induced behaviors in Mo pyrochlore oxides [S. Iguchi et al., Phys. Rev. Lett. 102, 136407 (2009)].Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let

Magnon Broadening Effects in Double Layered Manganite La_1.2 Sr_1.8 Mn_2 O_7

Magnon linewidth of La_1.2 Sr_1.8 Mn_2 O_7 near the Brillouin zone boundary is investigated from both theoretical and experimental points of view. Abrupt magnon broadening is ascribed to a strong magnon-phonon coupling. Magnon broadening observed in cubic perovskite manganites is also discussed.Comment: 4 pages + 1 jpeg figur

Electronic phase separation in the pyrochlore double-exchange model

Electronic phase separation and related inhomogeneity is ubiquitously seen in strongly-correlated systems. A typical example is found between ferromagnetic metal and antiferromagnetic insulator in CMR manganese oxides. Here we demonstrate that the geometrical frustration brings distinctive aspects into the phase separation phenomena. From Monte Carlo simulation and a simple energy comparison for the pyrochlore double-exchange model, we show that such phase separation takes place between ferromagnetic and paramagnetic metals. We discuss the relevance of our results to a spin-glassy metallic phase found in Mo pyrochlore oxides under external pressure.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. B (Rapid Commun.

Critical Exponents for the Ferromagnetism in Colossal Magnetoresistance Manganites

Critical phenomena of ferromagnetic transition in colossal magnetoresistance manganites are theoretically studied. Concerning the critical exponents for this transition, there still remains controversy among experimental results. In order to clarify intrinsic physics of the manganites through a comparison with theoretical prediction, we investigate the critical phenomena of double-exchange models by using finite-size scaling analysis on unbiased numerical results. As a result, we show that the critical exponents of the ferromagnetic transition of the three-dimensional double-exchange model is consistent with those of the Heisenberg model, but are distinct from the mean-field one.Comment: 3pages including 3 figures, submitted to Proc. ICNS 200