Influence of magnetic field on electrical and thermal transport in the hole doped ferromagnetic manganite: La(0.9)Na(0.1)MnO(3)

We report the magnetization (M), magnetostriction, electrical resistivity (ρ), thermal conductivity (κ) and thermopower (S) of polycrystalline La(0.9)Na(0.1)MnO(3) over a wide temperature range of 5 to 360 K. This sample undergoes a paramagnetic to ferromagnetic transition around T(C) = 274 K and electrical resistivity ρ shows an insulator–metal transition around T(IM) = 292 K. The sign of thermopower S is positive in the entire temperature range which indicates that majority charge carriers are holes. Thermopower exhibits a peak and thermal conductivity shows a dip at T(C) in the absence of magnetic field. Large difference between the experimentally determined activation energies of ρ and S in the insulating state indicates small polaron hopping dominant conduction above T(IM). Polaron formation above T(C), was further confirmed from the anomaly observed in thermal expansion (ΔL/L(0)) which shows a change in slope at T(IM). In the vicinity of T(C) at 3 T applied field, magneto-thermopower (∼61.5%) is larger than magnetothermal conductivity (∼12.7%) and magnetoresistance (∼49%).