Low-field magnetoresistive property of partially crystallized La0.5Sr0.5MnO3 thin films by pulsed laser deposition

La0.5Sr0.5MnO3 thin films deposited on (001) SrTiO3 substrates at different temperatures are prepared using pulsed laser deposition, and their electro - and magnetotransport properties are experimentally evaluated. The structu re analysis reveals that the thin films show amorphous, mixed amorphous/nan ocrystalline as well as epitaxial microstructures, respectively, depending on the deposition temperature. While the amorphous thin film exhibits varia ble range hopping conduction, the epitaxial sample is metal like and ferrom agnetic. Enhanced low-field magnetoresistance at low temperature for the mi crostructure in which the nanocrystalline phase and amorphous phase coexist is demonstrated. It is argued that the amorphous layer separating the neig hboring nanocrystals behaves as barrier for the spin-dependent tunneling, r esulting in enhanced magnetoresistance at low magnetic field. The modified two-channel model where the insulating conduction channel and the spin-orde red and metallic conduction channel coexist in parallel is employed to expl ain the magnetotransport phenomena. (C) 2000 American Institute of Physics. [S0021-8979(00)06418-5].