Hall Effect of La2/3(Ca,Pb)1/3MnO3 Single Crystals near the Critical Temperature

TL;DR

This study measures the Hall resistivity of La2/3(Ca,Pb)1/3MnO3 single crystals near the critical temperature, revealing temperature-dependent contributions and mechanisms to the anomalous Hall effect in these materials.

Contribution

It provides detailed analysis of the anomalous Hall effect in single crystals, highlighting the dominance of magnetic skew scattering and the proportionality between anomalous Hall coefficient and magnetoresistance.

Findings

Effective carrier density is higher than expected from doping.

Negative anomalous Hall contribution appears with increasing temperature.

The anomalous Hall coefficient is proportional to magnetoresistance.

Abstract

The Hall resistivity rho_{xy} of a La_{2/3}(Ca,Pb)_{1/3}MnO_3 single crystal has been measured as a function of temperature and field. The overall behavior is similar to that observed previously in thin-films. At 5 K, rho_{xy} is positive and linear in field, indicating that the anomalous contribution $R_S$ is negligible. However, the effective carrier density in a free electron model is n_{eff}=2.4 holes/Mn, even larger than the 0.85-1.9 holes/Mn reported for thin-films and far larger than the 0.33 holes/Mn expected from the doping level. As temperature increases, a strong, negative contribution to rho_{xy} appears, that we ascribe to R_S. Using detailed magnetization data, we separate the ordinary (\propto B) and anomalous (\propto M) contributions. Below T_C, R_S \propto rho_{xx}, indicating that magnetic skew scattering is the dominant mechanism in the metallic ferromagnetic regime. At and above the resistivity-peak temperature, we find that rho_{xy}/rho_{xx}M is a constant, independent of temperature and field. This implies that the anomalous Hall coefficient is proportional to the magnetoresistance. A different explanation based on two fluid model is also presented.