Surface Scaling of Magnetism in Cr:ZnO Dilute Magnetic Dielectric Thin Films

Measurements of the spontaneous magnetic moment and conductance of oxygen-saturated ZnO:Cr thin films and tunnel junctions show an exponential drop with increasing thickness. All films are in the insulating state. The type and concentration of dominant point defects in the bulk do not provide conditions for magnetic ordering, while surfaces play an important role in magnetism. We suggest that in film thicknesses below a characteristic length (~30 nm), surface states or enhanced concentration of point defects near the surface (oxygen vacancies or incorporated hydrogen) lead to surface magnetism. Ballistic tunneling is observed in junctions