Electrical and Magnetotransport Properties of

This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of La 0.7 Ca 0.3 Mn 1-x Co x O 3 (x = 0.09-0.17) prepared by solid-state reaction. Magnetic measurements versus temperature revealed gradual decrease of the magnetization (M) and Curie temperature (T C ) with increasing Co concentration (x). The T C values vary from 194 to 159 K as changing x from 0.09 to 0.17, respectively. H/M versus M 2 performances around T C prove the x = 0.09 sample undergoing a first-order magnetic phase transition (FOMT) while the samples with x ≥ 0.11 undergo a second-order magnetic phase transition (SOMT). The other with x = 0.10 is considered as a threshold concentration of the FOMT-SOMT transformation. Considering temperature dependences of resistivity, ρ(T), in the presence and absence of the magnetic field, the samples (excepting x = 0.17) exhibit a metal-insulator transition at T P = 60-160 K, which shifts toward lower temperatures with increasing x. the metallic-ferromagnetic region, the ρ(T) data are well fitted to a power function ρ(T) = ρ 0 + ρ 2 T 2 + ρ 4.5 T 4.5 . This indicates electron-electron and electron-magnon scattering processes are dominant at temperatures T θ D /2 (θ D is the Debye temperature) and T P