Effects of substrate-induced-strain on the structural and transport properties of La0.7Ca0.3MnO3 thin films

We have studied the structural and electrical properties of epitaxial La0.7Ca0.3MnO3 (LCMO) thin films prepared by metal organic deposition under different types and degrees of substrate-induced strain. 40-nm-thick films have been epitaxially grown on single-crystalline (LaAlO3)(0.3)-(SrAlTaO6)(0.7) (negligible tensile strain), SrTiO3 (tensile strain) and LaAlO3 (compressive strain) substrates. High-resolution X-ray diffraction and reciprocal space maps demonstrate a direct correlation between the crystalline quality and the substrate-induced strain. The electrical properties were found to be strongly dependent on the substrate used. The temperature dependence of resistivity curves was fitted using various approaches in different phases (below and above the ferromagnetic transition temperature T (P)). In the ferromagnetic metallic phase, rho(T) follows a T (alpha) power law. The obtained values of the coefficient alpha (3.5-4) indicate that the electrical transport in our films is a combination of spin wave scattering processes and electron-magnon or two-magnon scattering phenomena. In the paramagnetic insulator phase, the activation energy E (A) and the variable range hopping characteristics (characteristic temperature T (0)) were found to be strongly dependent on the strain-induced lattice mismatch between the LCMO and the substrate used.