Materials Science and Engineering B 109 (2004) 203–206 Synthesis and characterisation of La 1-x Na x MnO 3+δ thin films manganites I. Alessandri a,∗ , L. Malavasi b , E. Bontempi a , M.C. Mozzati c , C.B. Azzoni c , G. Flor b , L.E. Depero a a Dipartimento di Ingegneria Meccanica, INSTM, Laboratorio di Strutturistica Chimica, Università di Brescia, via Branze 38, 25123 Brescia, Italy b Dipartimento di Chimica Fisica “M. Rolla”, INSTM, Università di Pavia, V. le Taramelli 16, I-27100 Pavia, Italy c Dipartimento di Fisica “A. Volta”, INFM, Università di Pavia, via Bassi 6, I-27100 Pavia, Italy Abstract Optimally sodium doped lanthanum manganite (LNMO) thin films have been grown onto differently oriented NdGaO 3 single crystals substrates by means of radio-frequency (RF)-magnetron sputtering technique, in order to investigate the role of the strain imposed by lattice mismatch on the magnetotransport properties. Films deposited onto NdGaO 3 (1 1 0) experiment a slight in-plane compressive strain that can be tuned by the thickness and allows to achieve colossal magnetoresistive effects. On the contrary, the change of the substrate orientation induces an in-plane tensile strain, making the film insulating. Above observations are explained by considering the effect of distortions of the Mn–O coordination polyhedra. © 2003 Elsevier B.V. All rights reserved. Keywords: Sodium doped lanthanum manganites; Thin film; RF-magnetron sputtering; Substrate dependency; CMR; Strain; Double exchange 1. Introduction The discovery of the colossal magnetoresistance effect (CMR) in perovskite manganese oxides has triggered off a lot of attentions in this field because of the potential appli- cations in energy storage devices. The huge change in the resistance value exhibited by these materials in presence of external applied high magnetic fields has been usually ex- plained in terms of the double exchange (DE) mechanism proposed by Zener [1], recently corrected by taking into account both the strong influence of the lattice distortions and the magnetic phase separations [2,3]. Zener’s couples Mn 3+ /Mn 4+ can be created by doping the LaMnO 3 parent compound with alkaline or alkaline-earth ions or by chang- ing the oxygen stoichiometry. In order to answer the technological requests, several groups have recently investigated the behaviour of man- ganites prepared in thin film form [4]; all these cases point out the important role played by the substrate in ∗ Corresponding author. Tel.: +39-030-3715574; fax: +39-030-3702448. E-mail address: ivano.alessandri@ing.unibs.it (I. Alessandri). magnetoresistance tuning. Although some studies have been performed about the alkali-doped bulk phases, there are only a few works [5] concerning the thin film deposition and, to our knowledge, none of these have been performed by radio-frequency (RF)-magnetron sputtering; nevertheless, the possibility of manganite layers deposition over large areas in a comparatively cheap way makes this technique quite suitable for devices realisation. Sodium doped lan- thanum manganites La 1-x Na x MnO 3 (LNMO) display some interesting features: firstly, in theory, the same number of Mn 4+ produced by the usual divalent cation doping can be obtained with an half concentration of dopant, because of the +1 valence state of the alkali ion. Besides, the cationic radius of the sodium ion (1.39 Å) is very close to the lan- thanum one (1.36 Å) [6]; hence one may introduce a large amount of charge carrier without appreciable lattice dis- tortions and achieve the maximum integral transfer for the DE at about x = 0.16 doping level. In this paper we report the realisation of optimally-sodium doped lanthanum man- ganites thin films deposited by RF-magnetron sputtering onto differently oriented NdGaO 3 single-crystal substrates. Besides, we investigate the influence of the strain induced by the substrate on the magnetoresistance properties for epitaxially grown samples with different thickness. 0921-5107/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2003.10.046