Thermoelectric power of potassium doped lanthanum manganites at low temperatures |
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Authors: | Soma Das T.K. Dey |
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Affiliation: | Thermophysical Measurements Laboratory, Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur 721302, India |
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Abstract: | The temperature-dependent resistivity and thermoelectric power of monovalent (K) doped La1−xKxMnO3 polycrystalline pellets (x=0.05, 0.10 and 0.15) between 50 and 300 K are reported. K substitution enhances the conductivity of this system. Curie temperature (TC) also increases from 260 to 309 K with increasing K content. In the paramagnetic region (T>TC), the electrical resistivity is well represented by adiabatic polaron hopping, while in the ferromagnetic region (T<TC), the resistivity data show a nearly perfect fit for all the samples to an expression containing, the residual resistivity, spin-wave and two-magnon scattering and the term associated with small-polaron metallic conduction, which involves a relaxation time due to a soft optical phonon mode. Small polaron hopping mechanism is found to fit well to the thermoelectric power (S) data for T>TC whereas at low temperatures (T<TC) in ferromagnetic region (SFM), SFM is well explained with the spin-wave fluctuation and electron–magnon scattering. Both, resistivity and thermopower data over the entire temperature range (50–300 K) are also examined in light of a two-phase model based on an effective medium approximation. |
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Keywords: | 75.47.Gk 75.47.-m 72.15.Jf 71.30.+h 71.70.Ej |
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