Influence of magnetic field on electrical and thermal transport in the hole doped ferromagnetic manganite: La0.9Na0.1MnO3

We report the magnetization (M), magnetostriction, electrical resistivity (ρ), thermal conductivity (κ) and thermopower (S) of polycrystalline La_0.9Na_0.1MnO₃ 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%).