Small-polaron hopping conductivity in bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$

TL;DR

This study investigates the anisotropic resistivity in bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$, revealing that small polarons dominate electrical transport in the paramagnetic phase through temperature-dependent hopping mechanisms.

Contribution

The paper introduces a model linking resistivity and magnetization, demonstrating the critical role of small polarons in the transport properties of bilayer manganites.

Findings

Resistivity follows small polaron hopping above 218 K.

Out-of-plane resistivity obeys an Arrhenius law with the same activation energy.

Model accurately predicts resistivity behavior in magnetic fields.

Abstract

We report anisotropic resistivity measurements on a La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ single crystal over a temperature $T$ range from 2 to 400 K and in magnetic fields $H$ up to 14 T. For $T\geq 218$ K, the temperature dependence of the zero-field in-plane $\rho_{ab}(T)$ resistivity obeys the adiabatic small polaron hopping mechanism, while the out-of-plane $\rho_{c}(T)$ resistivity can be ascribed by an Arrhenius law with the same activation energy. Considering the magnetic character of the polarons and the close correlation between the resistivity and magnetization, we developed a model which allows the determination of $\rho_{ab,c}(H,T)$. The excellent agreement of the calculations with the measurements indicates that small polarons play an essential role in the electrical transport properties in the paramagnetic phase of bilayer manganites.