  The magnetic interaction of a pair of bound magnetic polarons (BMP) in
diluted magnetic semiconductors (DMS) is analyzed via a generalized
Hubbard-type Hamiltonian for two carriers in the presence of effective magnetic
fields arising from the magnetic polarization of their respective polarons. For
the case where the magnetic fields at the two sites have equal magnitude but
are allowed to have arbitrary directions, it is shown that the energy of the
two polarons is minimized for a ferromagnetic configuration of the carrier
spins (in contrast to the case of hydrogenic centers in nonmagnetic
semiconductors) if polaron fields are strong enough. A modified Heisenberg-type
Hamiltonian is constructed to describe the low energy states of the resulting
system.
