Influence of interface roughness on the exchange bias of Co/CoO multilayers

Abstract

The effect of interface roughness on the magnetic properties of ferromagnetic/antiferromagnetic multilayer has been studied by comparing the interfaces within identical multilayer (lower vs. upper) or from different Co/CoO multilayers (different deposition sequence). It has been found that for identical multilayer, the upper Co/CoO interfaces grow rougher and show stronger exchange bias than the lower Co/CoO interfaces. Structural analyses indicate that the successive layer deposition gives rise to a cumulative roughness at the upper interface, which affects the magnetic properties of ferromagnetic layer and its coupling to the antiferromagnetic layers. The interface roughness strengthens the interfacial exchange coupling by the increase of defect-generated uncompensated antiferromagnetic spins; such spins form coupling with the spins from Co layer at the interface. Due to the different coupling strength of each Co layer to the neighboring CoO layers, the multilayer showed distinct switching fields during the magnetization reversal process. Our results imply the possibility to control the strength of exchange bias, coercivity, and related magnetic properties by tuning the interface roughness.