  The feasibility of a single-domain ferromagnet based on uniaxial magnetic
ions was examined. For a noncentrosymmetric uniaxial magnetic ion of magnetic
moment at a site of local electric dipole moment p, it is unknown to date
whether the magnetic moment prefers to be parallel or antiparallel to the
electric dipole moment. The nature of this magnetoelectric interaction was
probed in terms of analogical reasoning based on the Rashba effect and density
functional calculations. We show that the magnetic and electric dipole moments
prefer an antiparallel arrangement, predict that Fe-doped CaZnOS is a
single-domain ferromagnet like a bar magnet, and find the probable cause for
the ferromagnetism and weak magnetization hysteresis in Fe-doped hexagonal ZnO
and ZnS at very low dopant concentrations.
