Cobalt oxide/ferromagnet bilayers: Exchange coupling and dominance of the antiferromagnet

Using cobalt oxide/ferromagnet bilayers with strong magnetic coupling, the nature of the interfacial exchange interaction in exchange bias systems has been investigated. For $\chem{Fe}$, $\chem{Co}$ and $\chem{Ni}$ as ferromagnetic materials, an almost linear temperature dependence of the exchange bias field $H_{\ab{E}}$ and a common blocking temperature $T_{\ab{B}}$ of 175$\un{K}$ have been found. Additionally, an inverse proportionality between $H_{\ab{E}}$ and the thickness of the ferromagnetic layer $t_{\ab{FM}}$ has been confirmed. The average coupling energies $\Delta E$ at T=10$\un{K}$ have been determined to 0.90, 1.02 and 0.80$\un{erg/cm^2}$ for $\chem{CoO/Fe}$, $\chem{CoO/Co}$ and $\chem{CoO/Ni}$ bilayers, respectively. The presently observed behavior strongly deviates from recent theoretical mean-field analysis and other experimental investigations on antiferromagnetic/ferromagnetic bilayers