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 Fe, Co and Ni as ferromagnetic materials, an almost linear temperature dependence of the exchange bias field H E and a common blocking temperature T B of 175 K have been found. Additionally, an inverse proportionality between H E and the thickness of the ferromagnetic layer t FM has been confirmed. The average coupling energies Δ E at T = 10 K have been determined to 0.90, 1.02 and 0.80 erg/cm 2 for CoO/Fe, CoO/Co and CoO/Ni bilayers, respectively. The presently observed behavior strongly deviates from recent theoretical mean-field analysis and other experimental investigations on antiferromagnetic/ferromagnetic bilayers.