Enhanced Magnetoresistance of (La_0.67Ca_0.33MnO₃) Composites Coated byZn_0.95Co_0.05O

La_0.7Ca_0.3MnO₃:xZn_0.95Co_0.05O (x = 0.0, 0.05, 0.1, 0.15 mol) composites are prepared by a sol-gel process. X-ray diffraction and energy diffraction spectroscopy reveal that there is no evidence of a reaction between the La_0.7Ca_0.3MnO₃(LCMO) and Zn_0.95Co_0.05O (ZCO). Magnetization M, Curie temperature T_C and metal-insulator transition temperatures T_p are observed to decrease with increasing ZCO content. Compared with x = 0.0, a great enhancement in the magnetoresistance (MR) is observed at around T_C for x = 0.05, 0.10, 0.15. Based on the tunneling MR and percolation models, this great change of MR is well explained.