Large Low-Field Magnetoresistance Observed in Polycrystalline La_0.7Ca_0.3MnO₃ Films

Large low-field magnetoresistance (LFMR) of ∆p/pH = 40% is obtained at 163 K within ±3000 Oe in a polycrystalline La_0.7Ca_0.3MnO₃ (LCMO) films prepared by pulsed laser deposition. The ratio ∆p/pH increases almost linearly with H in the measuring magnetic field range and the peak of LFMR ratios is observed near the resistivity peak temperature, which is different from the observation of spin-polarized intergrain tunnels. This experiment suggests that grain boundaries have large influences on the LFMR. The results indicate that a suitable film process can be used to increase the LFMR of LCMO films.