The Hall effect and hole densities in high Tc GaMnAs thin films
  By studying the Hall effect in a series of low resistivity Ga1-xMnxAs samples, accurate values for the hole density p, Mn concentration x, and Curie temperature Tc are obtained over the range 0.015=<x=<0.08. The hole density corresponds to 90% of the Mn concentration at low x, and has a maximum value of 1.0x10-27 m-3 when Tc=125K for x=0.06. This data allows the first meaningful comparison of mean field predicted Curie temperatures with experiment over a wide range of x. The theory is in qualitative agreement with experiment, but overestimates Tc at large x and underestimates TC at low x. 
K.W. Edmonds, K.Y. Wang, R.P. Campion, A.C. Neumann, C.T. Foxon, B.L.   Gallagher, and P.C. Main