Magnetoresistance, magnetothermopower, magnetothermal conductivity and magnetostriction in La1-xNaxMnO3 (0 ≤ x ≤ 0.05)

We report the influence of the magnetic field on electrical resistivity (rho), thermal conductivity (kappa), thermopower (S), and linear thermal expansion (Delta L/L-0) in La1-xNaxMnO3 series (x = 0, 0.01, 0.02, and 0.05) over a wide range of temperature. While LaMnO3 is an antiferromagnetic insulator, the doping with Na weakens the inter-planner antiferromagnetic coupling and transforms it into a ferromagnetic metal by promoting the double exchange coupling between Mn3+ and Mn4+ ions. rho and S show peaks, whereas, kappa shows a sudden increase at the onset of ferromagnetic spin ordering in the samples. Dominant charge carriers are holes in these doped compounds as indicated by the positive sign of S. High-temperature transport is explained in the context of the small polaron hopping model. External magnetic field influences thermal properties (S and kappa), and Delta L/L-0 mostly around the Curie temperature (TC), while it affects rho to as low as 10 K. Enhancement of kappa at the insulator-metal transition, on the application of external magnetic field, suggests a decrease in spin-wave scattering. The highest value of negative magnetoresistance (similar to 69.7%) and negative magnetothermopower (similar to 80.4%) is obtained for x = 0.02 and the value decreases for higher dopant concentration.

Automated summary

This study investigates the impact of magnetic field on electrical and thermal properties of La1-xNaxMnO3 series. It was found that at the onset of ferromagnetic spin ordering, resistivity and thermopower exhibit peaks while thermal conductivity shows a sudden increase. External magnetic field influences thermal properties and thermal expansion mostly around the Curie temperature, while its effect on resistivity extends to as low as 10 K.