  We have studied the evolution of the magnetic, electronic, and structural
properties of annealed epilayers of Ga1-xMnxAs grown by low temperature
molecular beam epitaxy. Annealing at the optimal temperature of 250 C for less
than 2 hours significantly enhances the conductivity and ferromagnetism, but
continuing the annealing for longer times suppresses both. These data indicate
that such annealing induces the defects in Ga1-xMnxAs to evolve through at
least two different processes, and they point to a complex interplay between
the different defects and ferromagnetism in this material.
