Metal-insulator transition temperature enhancement in La 0.7Ca 0.3MnO 3 thin films

Abstract

The effect of oxygen annealing on the structural and transport properties of La0.7 Ca0.3 MnO3 thin films deposited on SrTiO3 substrates has been investigated by x-ray diffraction analysis and resistive measurements. The as-grown films are fully tensile strained on the substrates and show a depressed metal-insulator transition temperature Tp =131 K. As the oxygen content is increased due to longer annealing times, significantly higher Tp are measured, up to 247 K. Correspondingly, an increase of the out-of-plane lattice parameter is observed while the in-plane lattice constants do not change with respect to the as-grown films, which prevents any interpretation of a Tp dependence on the strain. The large increase in Tp is then interpreted in terms of a combined effect of the Mn4+ Mn3+ ratio variation, the change in the carrier density in the a-b planes, and the increase in the hydrostatic strain with the oxygen annealing. © 2005 American Institute of Physics.