Electrical Transport and Giant Magnetoresistance in (1 - x) La0.67 Ca0.33 MnO3/x CuO Composites

Samples with nominal composition of (1 - x) La0.67Ca0.33MnO3 (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 (Tp), zero field peak resistivity (ρmax), and magnetoresistance (MR) properties of the composites. TP 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 Tp, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.