  We discuss the annealing-dependence of exchange bias in Ga1-xMnxAs epilayers
that are overgrown with Mn. Although pure Mn is a known antiferromagnet, we
find that the as-grown Mn overlayer does not produce any exchange coupling with
Ga1-xMnxAs. Rather, our studies indicate that annealing in air is essential for
creating the standard signatures of an exchange bias (a clear shift in the
magnetization hysteresis loop and an increased coercive field). We use x-ray
photoelectron spectroscopy to characterize the compositional depth profile of
both as-grown and rapid thermal annealed samples. These studies demonstrate
that the cleanest exchange bias arises when the Mn overlayer is completely
converted into MnO.
