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. Aruta; G. Balestrino; A. Tebano; G. Ghiringhelli; N. B. Brookes

doi:doi:10.1209/0295-5075/80/37003

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 L_{2, 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 e_g 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.

Cooperative enhancement of in-plane orbital ordering by oxygen deficiency and in-plane tensile strain in thin films

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