High-Temperature Hall Effect in Ga(1-x)Mn(x)As

The temperature dependence of the Hall coefficient of a series of ferromagnetic Ga(1-x)Mn(x)As samples is measured in the temperature range 80K < T < 500K. We model the Hall coefficient assuming a magnetic susceptibility given by the Curie-Weiss law, a spontaneous Hall coefficient proportional to rho_xx^2(T), and including a constant diamagnetic contribution in the susceptibility. For all low resistivity samples this model provides excellent fits to the measured data up to T=380K and allows extraction of the hole concentration (p). The calculated p are compared to alternative methods of determining hole densities in these materials: pulsed high magnetic field (up to 55 Tesla) technique at low temperatures (less than the Curie temperature), and electrochemical capacitance- voltage profiling. We find that the Anomalous Hall Effect (AHE) contribution to rho_xy is substantial even well above the Curie temperature. Measurements of the Hall effect in this temperature regime can be used as a testing ground for theoretical descriptions of transport in these materials. We find that our data are consistent with recently published theories of the AHE, but they are inconsistent with theoretical models previously used to describe the AHE in conventional magnetic materials.