Charge Transfer and Lattice Distortion in strained La0.7Ca0.3MnO3 and La0.8Ba0.2MnO3 Films on SrTiO3 Substrate

Lattice mismatches between La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO$ a$ = 3.86 Å) and La$_{0.8}$Ba$_{0.2}$MnO$_{3}$ (LBMO$ a$ = 3.89) CMR thin films and the substrate SrTiO$_{3}$ (00$l a $= 3.905 Å) induce a strong tensile strain that expands the in-plane lattice and shortens the out-of-plane lattice of films. The magnetic transition temperature (T$_{c})$ and the metal-insulator transition temperature (T$_{MI})$ are then suppressed dramatically in LCMO films and are raised in LBMO films. The possible causes of the contrary phenomena are examined by X-ray diffraction and HRXRD which indicate that the change of T$_{c}$ or T$_{MI}$ is highly possible due to the distortion in Mn-O-Mn chains, such as the bond length and angle, that induced the variation of orbital stability and the charge transfer in itinerant e$_{g}$ band.