Abstract
Exchange fields accompanying vertical magnetization shifts were observed in the epitaxial Zn Co0.07 O (dilute magnetic semiconductor)/NiO system after field cooling. Transitions of exchange fields and magnetization shifts were observed at 50 K, above which the magnetization shift disappeared and the exchange field was significantly reduced. Both the exchange field and the magnetization shift increased with increasing cooling-field strength at temperatures below 50 K, which might be attributed to the existence of "frozen" spins in ZnCoO. The observed linear dependence of the exchange field on the magnetization shift may directly elucidate the role of pinned spins on the exchange fields. © 2007 American Institute of Physics.