Effect of oxygen annealing on the magnetoresistance in La0.7Ca0.3MnO3epitaxial films

Epitaxially c-axis oriented thin films of La0.7Ca0.3MnO3 (LCMO) have been fabricated on (001) SrTiO3 and (001) LaAlO3 substrates by pulsed laser-ablated deposition technique. The physical properties of as-grown films are correlated with the structural nature of the substrate. The O2-annealed films grown on both substrates exhibit higher metal-insulator (M-I) transition temperatures (TMI) and larger magnetoresistance (MR) ratios than the corresponding as-grown films. On the other hand, the Ar-annealed films display enhanced MR without any noticeable change in TMI. We suggest that increase in TMI is mainly ascribed to oxygen incorporation whereas enhancement of MR is largely associated with microstructural change induced by thermal annealing. Structural and transport data reveal that post-annealing with O2 not only saturates the anion defect sites but also relieves structural strain, resulting in the enhancement of TMI and large MR.