Hall effect of La2/3(Ca,Pb)1/3MnO3 single crystals

The Hall resistivity ${\rho }_{\mathrm{xy}}$ of a ${\mathrm{La}}_{\text{2/3}}{\mathrm{(Ca,Pb)}}_{\text{1/3}}{\mathrm{MnO}}_3$ single crystal has been measured as a function of temperature and field. The overall behavior is similar to that observed previously in thin-film samples. At 5 K, ${\rho }_{\mathrm{xy}}$ is positive and linear in field, indicating that the anomalous contribution is negligible. However, the slope is small and, if a free carrier, single band model were used, the carrier density would be 2.4 holes per unit cell, even larger than the 0.85–1.9 holes per cell that have been reported using thin-film data and far larger than the 0.33 holes per cell expected from the doping level. As the temperature is increased, a strong, negative contribution to ${\rho }_{\mathrm{xy}}$ appears, due to the anomalous contribution to the Hall effect. Making use of a detailed measurement of the magnetization $\mathrm{M(B,T),}$ we separate the ordinary $\mathrm{(\propto B)}$ and anomalous $\mathrm{(\propto M)}$ contributions. The anomalous contribution is negative and proportional to the zero-field resistivity ${\rho }_{\mathrm{xx}}$ below $T_C,$ indicating that magnetic skew scattering is the dominant mechanism in the metallic ferromagnetic regime. Far above $T_C{\mathrm{,\hspace{0.5em}\rho }}_{\mathrm{xy}}$ shows a negative slope, and is to be associated with the hopping of small polarons. Above $T_C,$ the Hall mobility is field independent despite the changes in ${\rho }_{\mathrm{xx}}$ and nonlinear ${\rho }_{\mathrm{xy}}.$