Volume 80, Number 3, November 2007
|Number of page(s)||6|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||28 September 2007|
Cooperative enhancement of in-plane orbital ordering by oxygen deficiency and in-plane tensile strain in thin films
CNR-INFM Coherentia and Dipartimento di Ingegneria Meccanica, Università di Roma Tor Vergata Via del Politecnico 1, 00133 Roma, Italy
2 CNR-INFM Coherentia and Dipartimento di Fisica, Politecnico di Milano piazza Leonardo da Vinci 32, 20133 Milano, Italy
3 European Synchrotron Radiation Facility - BP220, 38043 Grenoble, France
Corresponding author: firstname.lastname@example.org
Accepted: 5 September 2007
The development of in-plane orbital ordering with oxygen deficiency is investigated in epitaxially strained thin films of grown under in-plane tensile strain on SrTiO3 substrates. The orbital character of states is directly probed by linear dichroism in X-ray absorption spectroscopy at the Mn and O K edges. The electrical transport measurements show a rapid decrease of the metal-insulator transition temperature and an increase of the polaronic activation energy when reducing the oxygen content. The diffraction measurements show a contraction of the average out-of-plane lattice parameter due to an enhancement of the regular distribution of the Mn3+ distorted octahedra in oxygen-deficient films. We show that the oxygen deficiency and the in-plane tensile strain cooperate to stabilize the in-plane orbital occupation: the oxygen deficiency is responsible for the increased number of Jahn-Teller distorted octahedra and the in-plane tensile strain drives the arrangement of such octahedra, favoring the in-plane confinement of the eg orbitals. Linear dichroism in X-ray absorption also demonstrates that the Mn O hybridization changes little with the oxygen content, thus confirming that the in-plane orbital ordering is the main factor influencing the transport properties.
PACS: 75.47.Lx – Manganites / 78.70.Dm – X-ray absorption spectra
© Europhysics Letters Association, 2007
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