The exchange bias $H_E$ of coupled polycrystalline films of antiferromagnetic CoO and ferromagnetic Co was significantly enhanced by the systematic substitution of nonmagnetic Mg for Co in CoO. Samples in which either Co or ${\mathrm{Co}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ were deposited first were investigated at temperatures from 10 to 300 K. With ${\mathrm{Co}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ on the bottom, the increased interfacial uncompensated spin density of the single antiferromagnetic domain ${\mathrm{Co}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ crystallites produced the enhanced $H_E$. With Co on the bottom, a thin interfacial oxide layer was primarily responsible for the strongly increased $H_E$.

• Received 3 September 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.117204