Electrical Transport and Giant Magnetoresistance in (1-x) La_(0.67) Ca_(0.33) MnO_3/xCuO Composites

摘要

Samples with nominal composition of (1 - x)La_(0.67) Ca_(0.33) MnO_3(LCMO)/xCuO (x =0%, 2%, 4% and 20 %) were made using a special experimental method. The temperature dependence of the resistivity (ρ) of the composites was investigated in the temperature range of 10 ～ 300 K and different magnetic fields of H = 0, 0.1, 0.3, 0.5, 1.0 and 3.0 T. The results showed that CuO percentage x had important effects on metal-insulator transition temperature (T_p), zero field peak resistivity (ρ_(max)), and magnetoresistance (MR) properties of the composites. T_p shifted sharply towards low temperature with the increase of x in the range of x ≤ 4 % , but was almost independent of x at high level of CuO content. Composites with x =4% and 20% exhibited similar electrical transmission behavior. Compared with pure LCMO, enhanced magnetoresistance could be clearly observed even in a quite low magnetic field of 0.3 T. For x = 4 % and 20 % samples, the MR value at 0.3 T could reach as high as ～ 88 % and ～ 90 % , respectively. XRD and SEM analysis showed that the substantial enhancement of MR, especially near T_p, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.