Effect of Cobalt on the Structure, Electrical, and Magnetic Properties of $\hbox {La}_{0.7}\hbox {Ca}_{0.3}\hbox {Mn}_{1-{\rm x}}\hbox {Co}_{\rm x}\hbox {O}_{3}$

We have investigated the structural, magnetic and electrical properties of Co-doped La_0.7Ca_0.3Mn_1-xCo_xO₃ (LCMCO) system using X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy, field cooled dc magnetization and magnetoresistance (MR) measurements. Polycrystalline bulk samples of La_0.7Ca_0.3Mn_1-xCo_xO₃ (0.0 les x les 0.05) were prepared by conventional solid state reaction method. XRD pattern infers that all samples show single phase polycrystalline behavior. The field cooled magnetization measured as a function of temperature indicates that all samples exhibit ferromagnetic (FM) to paramagnetic (PM) transition with decrease in the temperature. It is observed that FM to PM transition temperature (T_c) decreases with increase concentration of Co ions. The decrease in the T_c indicates that doping Co ions affect the magnetic ordering due to the decrease in Mn³⁺. The resistance measured as a function temperature demonstrates that all the samples display metal to semiconductor transition. The MR was measured in the presence of 7 T field. The MR value shifted to low temperature with the increment of Co concentration and then we can found that the high Co concentration is helpful to stabilize the MR ratio at low temperature.