Magnetoconductivity and Hall effects in La_0.67Ca_0.33MnO₃

The observed H² and \H\ dependence of the magnetoresistance above and below T_c, respectively, may be explained by general time-reversal symmetry considerations. We further find empirically that the saturation observed in the magnetoresistance is best fit by a simple resistor in series with a magnetoconductor: ρ(H) = ρ_∝+ 1/(σ₀+ γ\H\) for T<Tc and ρ(H) = ρ_∝+ 1/(σ₀ + βH²) for T >T_C. This provides a functional form to analyze and predict the magnetoresistance over a wide range of fields. This suggests that the underlying mechanism of "colossal magnetoresistance" may be magnetoconductive, not magnetoresistive. The magnetoresistance and Hall effects on an annealed epitaxial thin films of La_0.67Ca_0.33MnO₃ were measured at 0.9 T_c and 1.1 T_c. At low fields, anisotropic magnetoresistance plays a dominant role. The high field Hall effect shows holelike carriers above and below T_c. The apparent change in sign at low fields is likely due to the anomalous Hall effect.