We have investigated the thickness dependence of exchange bias (EB) in ultrathin epitaxial Cr/Fe/Ag(001) bilayers. The system features an artificially patterned structure consisting of coherently aligned nanometric ripples at the Cr/Fe buried interface. The patterning provides an abundance of preferentially aligned steps resulting in both morphological and magnetic uniaxial anisotropies. Increasing the Cr thickness the EB evolves from an uniaxially anisotropic state, in which its magnitude is a function of the field-cooling direction, to an isotropic behavior. We account for this phenomenon invoking a thickness-dependent variation in the spin structure of the antiferromagnet driven by the topological frustration at the stepped Cr/Fe interface.

• Received 12 January 2010

DOI:https://doi.org/10.1103/PhysRevB.81.224427