Electronic transport and magnetoresistivity of La_0.4Bi_0.1Ca_0.5-xSr_xMnO₃ (x = 0.1 and 0.2)

Electrical resistivity and magnetoresistive behaviour of bismuth-substituted lanthanum manganites La_0.4Bi_0.1Ca_0.5-xSr_xMnO₃ (x = 0.1 and 0.2) were systematically studied by varying the temperature from 2 to 300 K and the magnetic field up to 12 T. The samples were found to crystallize in rhombohedral structure and their morphology shows near-spherical nanosize crystallites. Charge ordering was observed in both the samples under zero field conditions and corresponding transition temperature T_CO was found to decrease with the increase of x. Resistivity measurements with magnetic field also showed suppression of magnetoresistivity (MR) with the increase of x and the maximum MR was found to be 98 and 93% for x = 0.1 and 0.2, respectively, at 10 T. In the high-temperature domain, the electronic transport was observed to be dominated by the variable range hopping mechanism for both the samples, whereas in the low-temperature domain the electrical conduction of x = 0.1 sample was observed to be contributed by various other electron scattering mechanisms. (author)