Hall-Effect Sign Anomaly and Small-Polaronic Conduction in (La_{1-x}Gd_x)_{0.67}Ca_{0.33}MnO_3

TL;DR

This study reveals an anomalous Hall effect in Gd-doped manganites, indicating small-polaronic conduction in the paramagnetic phase, with Hall coefficient behavior opposite to expectations based on doping and thermoelectric data.

Contribution

It provides experimental evidence of small-polaronic conduction and uncovers an unusual Hall effect behavior in Gd-doped manganites.

Findings

Hall coefficient shows Arrhenius behavior with activation energy close to 2/3 of conductivity.

Hall coefficient is electron-like despite hole-like conduction indicators.

Supports small-polaronic conduction mechanism in the paramagnetic regime.

Abstract

The Hall coefficient of Gd-doped La_{2/3}Ca_{1/3}MnO_3 exhibits Arrhenius behavior over a temperature range from 2T_c to 4T_c, with an activation energy very close to 2/3 that of the electrical conductivity. Although both the doping level and thermoelectric coefficient indicate hole-like conduction, the Hall coefficient is electron-like. This unusual result provides strong evidence in favor of small-polaronic conduction in the paramagnetic regime of the manganites.