The La0.75Sr0.2Mn1-xCoxO3 (0 ≤ X ≤ 1) Manganite-Cobaltites are
synthesized by sol-gel method and their structural, electrical and magnetic
properties are studied. After calcination over 800 ºC, all compounds were
crystallized in the perovskite rhombohedral structure ( R3C, Space group).
Due to nonstochiometery, some traces of the La2O3 phase were appeared in
final samples. Resistivity measurements of the samples between 77 and 328
K revealed that resistivity at first decreased and then increased by increasing
cobalt content. Also, magnetoresistance results in presence of external fields
up to 1.5 T exhibit negative magnetoresistance in all samples. The colossal
magneroresistance effect has been observed in all samples except the
samples without Mn. Variation of the resistivity and magnetoresistance of
the samples with Co content are described based on three following
mechanisms: spin scattering, charge compensation and distortion of metal–
oxygen-metal bonds. Magnetoresistance behavior of the samples are
evaluated based on (1) increased of the double exchange interaction, (2)
increased probability of inter-grain tunneling of the carriers, and (3)
decreased scattering of carriers from magnetic fluctuations mechanism in
the presence of applied field,