Giant magnetoresistance and unusual hysteresis behavior in La0.67Ca0.33MnO3/xCuO (x=20%) composite.

La_0.67Ca_0.33MnO₃(LCMO)/xCuO (x=0 and 20 mole %) composites were fabricated and investigated in detail for their electrical and magnetic transport properties. Compared with pure LCMO, the magnetoresistance (MR) effect for x=20% sample is substantially enhanced especially at the vicinity of T_IM, where T_IM is the transition temperature from insulator to metallic state. Application of even a low magnetic field of H=0.5 T leads to a MR value as large as ∼98%. It is interesting to note that at the same temperature region where substantial MR effect is obtained, considerable thermal and magnetic hystereses in resistivity (ρ) appear. The measurement of magnetization (M) versus magnetic field (H) also exhibits an unusual magnetic hysteresis. Due to the absence of these unusual hysteresis behaviors in pure LCMO, it is discussed that the abnormal experimental observations are attributed to the spin disorder especially at grain boundaries induced by the interaction product layer between LCMO and CuO. [ABSTRACT FROM AUTHOR]