  A close link between the charge transfer electronic structures and polarity
dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is
demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs
predicted from their charge transfer energies reproduce experimental trends
well. These results provide a unified basis for understanding both n- and
p-type ferromagnetic oxide DMSs.
