Strain dependence of the physical properties of epitaxial La0.7Ca0.3MnO3 thin films grown on LaAlO3 substrates

We present a systematic study of the structural, magnetic, electrical and magnetoresistive properties of La0.7Ca0.3MnO3 thin films epitaxially grown on LaAlO3 single crystalline substrates using metal organic deposition process. The evolutions of the lattice parameters and the corresponding strain as a function of the film thickness (20-80 nm) have been investigated using X-ray diffraction measurements. The films were found to be totally relaxed for a thickness around 60 nm. Magnetization and resistance measurements as a function of temperature revealed a direct correlation of the transition temperature from a ferromagnetic state to the paramagnetic state with the film thickness. The temperature dependence of the resistivity (ρ (T)) has been fitted using various theoretical approaches. Below the transition temperature (TP) the ρ (T) graphs were well fitted using the ρ(T) = ρ0 + ATα formula, in which the fitting parameters ρ0 and α have been used to clarify the conduction mechanism. Above TP, the ρ (T) graphs were found to be well fitted using different models including the VRH model and the small polaron model. A magnetoresistance of 91% was measured at 248 K for the for 60 nm thick film under an applied magnetic field of 7 T. As well as a non-volatile resistive switching capacity of 15% on Ag contacts deposited on top of this film.