Magnetoresistance and Hall Effect in the Ferromagnetic Semiconductor   GaMnAs
  The resistivity, temperature, and magnetic field dependence of the anomalous Hall effect in a series of metallic Ga1-xMnxAs thin films with 0.015=<x=<0.08 is presented. A quadratic dependence of the anomalous Hall resistance on the resistivity is observed, with a magnitude which is in agreement with Berry phase theories of the anomalous Hall effect in dilute magnetic semiconductors. 
K W Edmonds, R P Campion, K-Y Wang, A C Neumann, B L Gallagher, C T   Foxon, P C Main