Magnetic Anisotropy of Strained La 0.7 Sr 0.3 MnO 3 Thin Films Studied by MOKE
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Magnetic Anisotropy of Strained La0.7Sr0.3MnO3 Thin Films Studied by MOKE M. Koubaa1, A.M. Haghiri-Gosnet1, P. Lecoeur2, W. Prellier2 and B. Mercey2 Institut d'Electronique Fondamentale - IEF, Univ. Paris Sud, Bat 220, 91405 Orsay Cedex, France. 2 Laboratoire de Cristallographie et de Sciences des Matériaux, CRISMAT- ISMRA, CNRS UMR 6508, 6 bd du Maréchal Juin, 14050 Caen Cedex, France. 1
ABSTRACT The effects of the growth conditions and the lattice strains of pulsed laser deposited (PLD) La0.7Sr0.3MnO3 (LSMO) thin films upon the magnetic behavior have been studied using magneto-optical Kerr effect (MOKE) at room temperature. First, the structural quality of the films was investigated by XRD and the surface morphology was studied using AFM. It is shown that both surface morphology and crystallinity are optimized when the target-to-substrate distance and the oxygen pressure are chosen in agreement with a PD3 scaling law. Secondly, hysteresis loops have been recorded along the [100], [110] and [001] directions and the easy directions of magnetization have been determined for both stress states, i.e. tension on SrTiO3 and compression on LaAlO3. In tensile films, the whole plane is found to be easy, whereas, in compressive films, the easy axis should be an intermediate direction between the film’s plane and its normal. Moreover, tensile films deposited under optimized growth conditions exhibit the largest anisotropy coefficient (K1eff = -6.9×105 erg/cm3). INTRODUCTION The colossal magnetoresistance (CMR) effect in manganite thin films has renewed interest due to their potential applications in magnetic devices [1-2]. Among these CMR compounds, La0.7Sr0.3MnO3 (LSMO), is the most interesting material because it has not only the lowest resistivity and the highest Curie temperature but it is also ferromagnetic metallic at room temperature (RT). Epitaxial thin films of LSMO grown on single crystal substrates exhibit a magnetic behavior different from the intrinsic properties of the bulk materials [3]. Suzuki et al. report that the magnetic anisotropy is dominated by stress effects due to the lattice mismatch between the film and the substrate [4]. On the other hand, we have recently observed that the morphology of thin LSMO films is fully dependent of the pulsed laser deposition (PLD) parameters, that are the oxygen pressure P and the target-to-substrate distance D [5]. Thus, we propose to study the precise role of P and D on the magnetic properties and more particularly on the shape of hysteresis loops. LSMO thin films have been grown under different P and D values on two types of (001) substrates, SrTiO3 (STO) and LaAlO3 (LAO). The first part of this paper studies the influence of P and D on the crystallinity. The second part reports a systematic magneto-optical Kerr effect (MOKE) study of the magnetic anisotropy. EXPERIMENTAL DETAILS LSMO thin films (500Å) were grown on (001) STO and (001) LAO substrates using the PLD technique (Lambda Physik KrF , λ = 248nm, repetition rate 2Hz, fluence close to 2 J/cm2) [6]. F9.9.1
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