Issue Eur. Phys. J. B Volume 34, Number 2, July II 2003 Page(s) 179 - 192 Section Solid and Condensed State Physics DOI 10.1140/epjb/e2003-00210-8 Published online 04 August 2003

Eur. Phys. J. B 34, 179-192 (2003)
DOI: 10.1140/epjb/e2003-00210-8

EELS study of interfaces in magnetoresistive LSMO/STO/LSMO tunnel junctions

L. Samet^{1, 2}, D. Imhoff¹, J.-L. Maurice³, J.-P. Contour³, A. Gloter¹, T. Manoubi², A. Fert³ and C. Colliex<sup>1

1</sup>  Laboratoire de Physique des Solides (UMR CNRS 8502) , bâtiment 510, Université Paris-Sud, 91405 Orsay, France
²  LPMC, Faculté des Sciences de Tunis, Campus Universitaire, 1060 Tunis, Tunisia
³  UMR de Physique CNRS/Thalès, Domaine de Corbeville, 91404 Orsay, France

imhoff@lps.u-psud.fr

(Received 3 January 2003 / Received in final form 14 April 2003 Published online 4 August 2003 )

Abstract
A magnetic tunnel junction consists of two ferromagnetic conducting electrodes separated by an insulating thin layer. The performance of such a system strikingly depends on the last conducting atomic layers in contact with the insulator. Consequently, the present paper reports a nanoscale electron energy loss spectroscopy (EELS) study, which has been performed across a couple of La _0.66Sr _0.33MnO ₃,/SrTiO ₃/La _0.66Sr _0.33MnO ₃ tunnel junctions with different barrier thicknesses (1.5 nm and 5 nm respectively). It aims at determining not only the chemical composition in the interface areas, but also the effect of the neighbouring atoms on their electronic structure. Using recent improvements in the STEM-EELS data acquisition and processing techniques (systematic use of spectrum-line and spectrum-image modes, multivariate statistical analysis, 2D energy deconvolution schemes, etc.), the local chemical information is better extracted with shorter acquisition times, while the large increase of the data set contributes to validate the results. Within the accuracy level of these measurements, the elemental composition of the different phases remains stable up to the interfaces with no evidence of extra doping. Furthermore, weak changes on the Mn-2 p edge fine structures (weak shift to lower energy loss values and extra splitting on the top of the Mn L ₃ line are observed on all the interfaces. They are interpreted as a consequence of a slight reduction of the local Mn valence likely accompanied by a strain induced change in local symmetry. The discussion is focussed on all spectral changes identified at a (sub)nanometer scale and their potential effects on the degradation of magnetic and transport properties measured, close to room temperature, at a macroscopic level.

PACS
75.45.+j - Macroscopic quantum phenomena in magnetic systems.
82.80.Pv - Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.).
68.37.Lp - Transmission electron microscopy (TEM) (including STEM, HRTEM, etc.).
85.30.Mn - Junction breakdown and tunneling devices (including resonance tunneling devices) .

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003

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