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

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.