Hall effect of La-2/3(Ca,Pb)(1/3)MnO3 single crystals

The Hall resistivity rho(xy) of a La-2/3(Ca, Pb)(1/3)MnO3 single crystal ha s been measured as a function of temperature and field. The overall behavio r is similar to that observed previously in thin-film samples. At 5 K, rho( xy) is positive and linear in field, indicating that the anomalous contribu tion is negligible. However, the slope is small and, if a free carrier, sin gle band model were used, the carrier density would be 2.4 holes per unit c ell, even larger than the 0.85-1.9 holes per cell that have been reported u sing thin-film data and far larger than the 0.33 holes per cell expected fr om the doping level. As the temperature is increased, a strong, negative co ntribution to rho(xy) appears, due to the anomalous contribution to the Hal l effect. Making use of a detailed measurement of the magnetization M (B,T) , we separate the ordinary (proportional to B) and anomalous (proportional to M) contributions. The anomalous contribution is negative and proportiona l to the zero-field resistivity rho(xx) below T-C, indicating that magnetic skew scattering is the dominant mechanism in the metallic ferromagnetic re gime. Far above T-C, rho(xy) shows a negative slope, and is to be associate d with the hopping of small polarons. Above T-C, the Hall mobility is field independent despite the changes in rho(xx) and nonlinear rho(xy). (C) 1999 American Institute of Physics. [S0021-8979(99)20508-7].