Abstract
The modifications in electrical and magnetic properties of polycrystalline bulk La 0.7Ca 0.3Mn 1− x T x O 3 (T=Fe, Ga) samples at relatively higher doping concentration ( x=0.08–0.12) are investigated. All the synthesized, single phase samples were subjected to resistivity measurements in the temperature range 50–300 K. No insulator–metal transition ( T P) was observed for Fe doped samples with x=0.12. For all the other samples the transition temperature decreased with increase in doping concentration. The small polaron hoping energy was found to increase, rather slowly, with increase in doping concentration. The effect on magnetic properties is also prominently observed with respect to doping element and doping concentration. Interestingly, with the increase in doping concentration, the Curie temperature ( T C) and T P separate out significantly indicating decoupling of electric and magnetic properties. Changes in these properties have been analyzed on the basis of magnetic disorder introduced in the system due to the magnetic and nonmagnetic nature of these ions rather than strong lattice effects which is insignificant due to similar ionic radii of Fe +3 and Ga +3 when compared to that of Mn +3.
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