Issue
EPL
Volume 80, Number 3, November 2007
Article Number 37003
Number of page(s) 6
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/80/37003
Published online 28 September 2007
EPL, 80 (2007) 37003
DOI: 10.1209/0295-5075/80/37003

Cooperative enhancement of in-plane orbital ordering by oxygen deficiency and in-plane tensile strain in $\mathrm{La}_{0.7}\mathrm{Sr}_{0.3}\mathrm{MnO}_{3-\delta}$ thin films

C. 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

aruta@na.infn.it

received 13 July 2007; accepted in final form 5 September 2007; published November 2007
published online 28 September 2007

Abstract
The development of in-plane orbital ordering with oxygen deficiency is investigated in epitaxially strained thin films of $\mathrm{La}_{0.7}\mathrm{Sr}_{0.3}\mathrm{MnO}_{3-\delta}$ 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.

PACS
75.47.Lx - Manganites.
78.70.Dm - X-ray absorption spectra.

© Europhysics Letters Association 2007