Magnetoresistance effect in La0.7Sr0.3MnO3 thin films fabricated by using pulsed laser deposition

La0.7Sr0.3MnO3 thin films were fabricated onto (100) n-Si substrates by using pulsed laser deposition (PLD). The thickness of the films was controlled from similar to 30 nm to 100 nm by varying deposition time. The deposited films were then annealed at 600 degrees C for 5 h. Room-temperature X-ray patterns verifed that the films had a La0.7Sr0.3MnO3 single phase as did the target. The crystalline orientation of the films was influenced by the films thickness. Thinner films were more oriented in the (104) direction. The Magnetoresistance (MR) measured at 300 K for all the films exhibited a pure DE behavior that depended on the films thickness. A nonlinear field dependence of the magnetoresistance was observed in the temperature region far below T-C. This obtained result could not be explained by the DE mechanism. Fitting experimental data to the spin polarized tunneling model, we attributed the dominated low-field MR below T-C to spin polarized tunneling between grain boundaries.