Abstract
AbstractPolycrystalline bulk samples of double layered (DL) colossal magnetoresistive (CMR) manganites R1.2Sr1.8Mn2O7(R = La, Pr, Sm) were prepared by sol-gel method to study the effect of size of lanthanide ion on their magnetotransport properties. The electrical resistivity of the samples was investigated in the temperature range of 70 K to 300 K at different magnetic fields. The samples LSMO and PSMO show insulator-to-metal transition (IMT) behavior, while SSMO sample exhibits insulating behavior in the entire temperature range with a very large value of resistivity. The insulator-to-metal transition temperature (TIM) decreases from 123 K (LSMO) to 90 K (PSMO) and disappears in SSMO sample. To explain the electrical transport above TIM, the temperature dependent resistivity data (T > TIM) of all the samples were fitted to the equations of different conduction models. The results indicate that the conduction at T > TIMis due to Mott variable range hopping (VRH) mechanism in the LSMO and PSMO samples, while Efros-Shkloskii (ES) type of VRH model dominates the conduction process in the SSMO sample. All the three samples show increasing magnetoresistance (MR) even below TIMand the maximum MR is shown by LSMO (39 % at 75 K, 3 T).
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