Low-Field Magnetoresistance of La0.7Sr0.3MnO3 Thin Film Fabricated by Using Pulsed-Laser Deposition

La0.7Sr0.3MnO3 thin films were grown on n-Si (100) substrates in a high vacuum by using pulsed-laser deposition. The magnetic and the transport properties were investigated. The results showed that large magnetoresistance (MR) effects were achieved near and far below the ferromagnetic transition temperature T-C. At low temperatures, the MR(H) curves are divided into two parts. In the high-magnetic-field region, the MR varies linearly with H and the partial derivative MR/partial derivative H value is nearly independent of temperature. At low magnetic fields, however, the MR changes nonlinearly with magnetic field and is strongly temperature-dependent. The low-field MR(H) can be well fitted by assuming it to be proportional to M-2, suggesting that the main mechanism for the low-field MR effect at low temperatures is attributed to the tunneling of spin-polarized electrons between ferromagnetic grains.