Effect of substitution of cobalt on crystal structure and magnetoresistance of La0.75Sr0.2Mn1-xCoxO3 compositions, prepared by sol-gel technique

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 (, 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,