Charge Transfer Excited State Contributions to Polarity Dependent   Ferromagnetism in ZnO Diluted Magnetic Semiconductors
  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. 
Kevin R. Kittilstved, William K. Liu, and Daniel R. Gamelin