Abstract
Polycrystalline samples of double layered (DL) manganite system La 1.2( Sr 1-x Ba x)1.8 Mn 2 O 7(0.0≤×≤0.4) were prepared by the sol-gel method. The anisotropic lattice expansion is observed with the substitution of Ba 2+ into Sr 2+ sites. The electrical resistivity and magnetoresistance (MR) measurements were carried out over the temperature range 4.2 K–300 K. The substitution of Ba results in the suppression of T IM , insulator-to-metal transition temperature. A low temperature upturn of resistivity is seen in all the samples of the system, which is attributed to the spin-glass-like transition. The conduction mechanism above T IM is explained by Mott variable range hopping (VRH) mechanism. The variation of MR with temperature and applied magnetic field is discussed. From the temperature dependent MR curves, it is observed that the large MR values are present over a wide temperature range and the maximum MR values occur at [Formula: see text]. The x=0.4 sample exhibits ~31% of MR with the application of a mere 0.4 T field at 5 K, which accounts for ~35% enhancement of MR of parent compound (~23% of MR% at 0.4 T at 5 K). The MR — H data is fitted to the power law ρ = ρ0-αHn, and it is found that the low temperature MR varies as square root of the applied magnetic field, as expected in conventional metals.
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