Impurity Conduction and Magnetic Polarons in Antiferromagnetic Oxides

Low-temperature transport and magnetization measurements for the antiferromagnets SrMnO(3) and CaMnO(3) identify an impurity band of mobile states separated by energy E from electrons bound in Coulombic potentials. Very weak electric fields are sufficient to excite bound electrons to the impurity band, increasing the mobile carrier concentration by more than three orders of magnitude. The data argue against the formation of self-trapped magnetic polarons (MPs) predicted by theory, and rather imply that bound MPs become stable only for kT<<E.Comment: 4 pp., 4 fig

Relationship between macroscopic physical properties and local distortions of low doping La{1-x}Ca{x}MnO3: an EXAFS study

A temperature-dependent EXAFS investigation of La{1-x}Ca{x}MnO3 is presented for the concentration range that spans the ferromagnetic-insulator (FMI) to ferromagnetic-metal (FMM) transition region, x = 0.16-0.22. The samples are insulating for x = 0.16-0.2 and show a metal/insulator transition for x = 0.22. All samples are ferromagnetic although the saturation magnetization for the 16% Ca sample is only ~ 70% of the expected value at 0.4T. We find that the FMI samples have similar correlations between changes in the local Mn-O distortions and the magnetization as observed previously for the colossal magnetoresistance (CMR) samples (0.2 < x < 0.5) - except that the FMI samples never become fully magnetized. The data show that there are at least two distinct types of distortions. The initial distortions removed as the insulating sample becomes magnetized are small and provides direct evidence that roughly 50% of the Mn sites have a small distortion/site and are magnetized first. The large remaining Mn-O distortions at low T are attributed to a small fraction of Jahn-Teller-distorted Mn sites that are either antiferromagnetically ordered or unmagnetized. Thus the insulating samples are very similar to the behavior of the CMR samples up to the point at which the M/I transition occurs for the CMR materials. The lack of metallic conductivity for x <= 0.2, when 50% or more of the sample is magnetic, implies that there must be preferred magnetized Mn sites and that such sites do not percolate at these concentrations.Comment: 27 pages, 8 figures, to be submitted to Phys. Rev.

Stoichiometry, structure, and transport in the quasi-one-dimensional metal, Li(0.9)Mo(6)O(17)

A correlation between lattice parameters, oxygen composition, and the thermoelectric and Hall coefficients is presented for single-crystal Li(0.9)Mo(6)O(17), a quasi-one-dimensional (Q1D) metallic compound. The possibility that this compound is a compensated metal is discussed in light of a substantial variability observed in the literature for these transport coefficients.Comment: 5 pages, 4 Figures; Phys. Rev. B (in press

Coupling of phonons with orbital dynamics and magnetism in CuSb2O6

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOStrongly interacting phonons and orbital excitations are observed in the same energy range for CuSb2O6, unlocking a so-far unexplored type of electron-phonon interaction. An orbital wave at similar to 550 cm(-1) softens on warming and strongly interferes with a phonon at similar to 500 cm(-1), giving rise to a merged excitation of mixed character. An electronic continuum grows on warming to the orbital ordering temperature T-oo = 400 K, generating an important phonon decay channel. This direct and simultaneous observation of orbital and vibrational excitations reveals details of their combined dynamics. In addition, phonon frequency anomalies due to magnetic correlations are observed below similar to 150 K, much above the three-dimensional magnetic ordering temperature T-N(3D) = 8.5 K, confirming one-dimensional magnetic correlations along Cu-O-O-Cu linear chains in the paramagnetic state.971715FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO2012/04870-7Sem informaçãoSem informaçãoAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

Mandarin Ducks in Myth and Legend

This is where the abstract of this record would appear. This is only demonstration data