  Magneto-optical properties of ZnO:Co and ZnO:Ni films were measured.
Magnetization measurements show that some of the films are paramagnetic and
others are ferromagnetic. Magnetic circular dichroism clarified that Zn1-xCoxO
and Zn1-xNixO included in samples are paramagnetic diluted magnetic
semiconductors. Ferromagnetic precipitations seem to be responsible for the
observed ferromagnetic behaviors. Criteria to judge the ferromagnetic DMS are
also discussed.
