Magnetotransport properties in La1-xCaxMnO3 (x=0.33, 0.5) thin films deposited on different substrates.

Magnetotransport properties of La_1-xCa_xMnO₃ (x=0.33, 0.5) thin films on different substrates are systematically studied. Due to the different lattice-substrate mismatch between films and substrates, compressive, and tensile epitaxial strain can be induced, respectively. The structure distortion induced by the strain with different sign influences the transport property and magnetoresistance. The tensile strain induces an increase of resistivity and magnetoresistance, while the resistivity peak temperature decreases. Compressive strain leads to a contrary behavior. The microstructure of films is also dominated by the lattice-substrate mismatch strongly. The inhomogeneities and different mixed domain structure induce the broadening of magnetic transition in films on SrTiO₃ and NdGaO₃, and a sharp increase in magnetoresistance in La_0.67Ca_0.33MnO₃ films with increasing field. In addition, the low temperature metal–insulator transition in the resistivity of La_0.5Ca_0.5MnO₃ film on LaAlO₃ also indicates the sample inhomogeneities. The suppression of the charge-ordering state in La_0.5Ca_0.5MnO₃ films is mainly dominated by the magnetic field, whereas the effect of the lattice-substrate mismatch is weak. It is due to the origin of the charge-ordering state. When the charge-ordering state is completely suppressed, the effect of lattice-substrate mismatch on charge transport and magnetoresistance shows up obviously. [ABSTRACT FROM AUTHOR]