Abstract
By means of extended magnetic after-effect (MAE) and electric resistivity measurements (4 K<T<300 K), polycrystalline La0.8Ca0.2MnO3 has been identified below the Curie temperature (TC190 K), as a ferromagnetic, metal-like band-conductor and above TC as a paramagnetic semiconductor, displaying a huge, magnetic order-related resistivity peak near 200 K. Weakly structured MAEs, occurring in the temperature range 4 K<T<190 K with logarithmic time dependence, are attributed to continuously superimposed Debye processes with activation enthalpy spectra in the range 0.008<Q<0.5 eV and pre-exponential factors, 0, of 10-12 to 10-11s. These enthalpy spectra are related to electrons which, due to localization at Jahn-Teller stabilized Mn3+-ions, are able to contribute to MAEs only after thermal activation. According to our analysis, charge transport in the semiconducting phase, above TC, is supported by hopping of small polarons with activation enthalpies, Q, of about 0.15 eV.
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