  We investigate the effect of an external magnetic field on the physical
properties of the acceptor hole states associated with single Mn acceptors
placed near the (110) surface of GaAs. Crosssectional scanning tunneling
microscopy images of the acceptor local density of states (LDOS) show that the
strongly anisotropic hole wavefunction is not significantly affected by a
magnetic field up to 6 T. These experimental results are supported by
theoretical calculations based on a tightbinding model of Mn acceptors in GaAs.
For Mn acceptors on the (110) surface and the subsurfaces immediately
underneath, we find that an applied magnetic field modifies significantly the
magnetic anisotropy landscape. However the acceptor hole wavefunction is
strongly localized around the Mn and the LDOS is quite independent of the
direction of the Mn magnetic moment. On the other hand, for Mn acceptors placed
on deeper layers below the surface, the acceptor hole wavefunction is more
delocalized and the corresponding LDOS is much more sensitive on the direction
of the Mn magnetic moment. However the magnetic anisotropy energy for these
magnetic impurities is large (up to 15 meV), and a magnetic field of 10 T can
hardly change the landscape and rotate the direction of the Mn magnetic moment
away from its easy axis. We predict that substantially larger magnetic fields
are required to observe a significant field-dependence of the tunneling current
for impurities located several layers below the GaAs surface.
