Resistivity, Giant Magnetoresistance And Thermopower In La0.7Sr0.3Mno3 Showing A Large Difference In Temperatures Corresponding To The Ferromagnetic Transition And The Insulator-Metal Transition

Abstract

La0.7Sr0.3MnO3 samples prepared by heating the precursor gel at different temperatures in the 873 – 1473 K range show nearly the same ferromagnetic transition temperature (Tc ≈ 392±4 K), but the insulator-metal like transition temperatures (Tp) are significantly lower (≈ 170 K) than the corresponding Tcs in the samples annealed at lower temperatures (873 K and 1073 K). Magnetoresistance shows a peak only in the sample where Tp ≈ Tc. Thermopower (S) is large and negative for the samples annealed at lower temperatures, but it is low, exhibiting a change of sign with temperature for the sample annealed at 1473 K.