Mechanical and Electronic Properties of Ferromagnetic GaMnAs Using   Ultrafast Coherent Acoustic Phonons
  Ultrafast two-color pump-probe measurements, involving coherent acoustic phonon (CAP) waves, have provided information simultaneously on the mechanical properties and on the electronic structure of ferromagnetic GaMnAs. The elastic constant C11 of Ga1-xMnxAs (0.03<x<0.07) are observed to be systematically smaller than those of GaAs. Both C11 and Vs of GaMnAs are found to increase with temperature (78 K<T<295 K), again in contrast to the opposite behavior in GaAs. In addition, the fundamental bandgap (at E0 critical point) of Ga1-xMnxAs is found to shift slightly to higher energies with Mn concentration. 
J. Qi, J. A. Yan, H. Park, A. Steigerwald, Y. Xu, S. N. Gilbert, X.   Liu, J. K. Furdyna, S. T. Pantelides, N. Tolk