Cooperative enhancement of in-plane orbital ordering by oxygen deficiency and in-plane tensile strain in thin filmsC. Aruta1, G. Balestrino1, A. Tebano1, G. Ghiringhelli2 and N. B. Brookes3
1 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
received 13 July 2007; accepted in final form 5 September 2007; published November 2007
published online 28 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 3d states is directly probed by linear dichroism in X-ray absorption spectroscopy at the Mn L2, 3 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 3d/O 2p hybridization changes little with the oxygen content, thus confirming that the in-plane orbital ordering is the main factor influencing the transport properties.
75.47.Lx - Manganites.
78.70.Dm - X-ray absorption spectra.
© Europhysics Letters Association 2007