Structure and Magnetotransport Properties of La_2/3Ca_1/3MnO₃ Thin Films Prepared by Pulsed Laser Deposition

Abstract

La_1-xCa_xMnO_3-δ (LCMO) thin films are grown by pulsed laser deposition on a (100) SrTiO₃ substrate at temperatures between 530°C and 890°C. The magnetotransport properties show a high negative magnetoresistance and a shift of the maximum of the R(T) curve as function of temperature. The Curie temperature changes with deposition temperature and film quality in the range of 100-220K. The film quality is characterised by X-ray diffraction and transmission electron microscopy (TEM); film and target compositions were verified by atomic emission spectroscopy. The local structure of the film depends on the growth conditions and substrate temperature. TEM reveals a slight distortion of the film leading to a breakdown of the symmetry from orthorhombic to monoclinic. At the highest growth temperatures, a well defined interface is observed within the LCMO film, parallel to the substrate surface; this interface divides the film into two lamellae with a different microstructure. The lamella close to the substrate is perfectly coherent with the substrate, suggesting that it is strained as a result of the lattice parameter mismatch; the upper lamella shows a typical domain structure with unusual translation interfaces characterised by a displacement vector of the type 1/2[010]_m and 1/2[001]_m when referred to the monoclinic lattice.