Manganese oxides with perovskite structure play a special role in the field of strongly correlated systems since their peculiar magnetic transport properties. These are due to ferromagnetic double-exchange (DE) and antiferromagnetic super-exchange (SE) interaction among Mn ions, and strong electron-phonon interaction (small and/or large polarons). The balance among these interactions is mainly determined by local atomic structure surrounding Mn ions, characterized by Jahn-Teller (JT) distortions of MnO6 octahedra. Therefore the sensitivity to the short-range order of x-ray absorption spectroscopy (XAS) makes this technique suited to study these compounds as demonstrated by the wide recent literature. In particular the analysis of the XANES region could provide topological information useful to deeply understand the physics of manganites. This work reports the first attempt to a quantitative analysis of Mn K edge XANES on CaMnO3 and LaMnO3 perovskite samples. The local structures obtained by fitting the XANES data are compared with structural models derived by standard EXAFS analysis and diffraction (x-ray and neutron) data analysis. In CaMnO3 the average structure derived from XANES results in good agreement with EXAFS analysis and with the structure found by diffraction. This strengthens the confidence on the MXAN method. In LaMnO3 XAS results reproduce the main structural features as given by XRD, but both EXAFS and XANES suggest reduced Mn-O apical distance, resulting in a Jahn-Teller distortion 15-20 % reduced compared with the coherent distortion obtained by neutron diffraction.
Monesi, C., Bardelli, F., Meneghini, C., Mobilio, S., Benfatto, M., Manju, U., et al. (2004). Mn-K edge XANES structural refinement in manganese perovskites.
Mn-K edge XANES structural refinement in manganese perovskites
MONESI, CLAUDIA;MENEGHINI, CARLO;MOBILIO, Settimio;
2004-01-01
Abstract
Manganese oxides with perovskite structure play a special role in the field of strongly correlated systems since their peculiar magnetic transport properties. These are due to ferromagnetic double-exchange (DE) and antiferromagnetic super-exchange (SE) interaction among Mn ions, and strong electron-phonon interaction (small and/or large polarons). The balance among these interactions is mainly determined by local atomic structure surrounding Mn ions, characterized by Jahn-Teller (JT) distortions of MnO6 octahedra. Therefore the sensitivity to the short-range order of x-ray absorption spectroscopy (XAS) makes this technique suited to study these compounds as demonstrated by the wide recent literature. In particular the analysis of the XANES region could provide topological information useful to deeply understand the physics of manganites. This work reports the first attempt to a quantitative analysis of Mn K edge XANES on CaMnO3 and LaMnO3 perovskite samples. The local structures obtained by fitting the XANES data are compared with structural models derived by standard EXAFS analysis and diffraction (x-ray and neutron) data analysis. In CaMnO3 the average structure derived from XANES results in good agreement with EXAFS analysis and with the structure found by diffraction. This strengthens the confidence on the MXAN method. In LaMnO3 XAS results reproduce the main structural features as given by XRD, but both EXAFS and XANES suggest reduced Mn-O apical distance, resulting in a Jahn-Teller distortion 15-20 % reduced compared with the coherent distortion obtained by neutron diffraction.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
