Competing Effects of Magnetocrystalline Anisotropy and Exchange Bias in Epitaxial Fe/IrMn Bilayers

We systematically investigated the possible magnetization reversal behavior in well-characterized, epitaxial, Fe/IrMn exchange-biased bilayers as a function of the antiferromagnetic (AF) layer thickness. Several kinds of multistep loops were observed for the samples measured at various field orientations. The angular dependence of the switching fields, observed using longitudinal and transverse magneto-optic Kerr effect, were shown to depend on the competition between the magnetocrystalline anisotropy and the exchange bias (EB). A modified “effective field” model was applied to quantitatively describe the evolution of the magnetic behavior and correctly predict the occurrence of different magnetic switching processes. The dependence of the effective anisotropy fields on the AF layer thickness directly reflects the competing effects of the pinned and rotatable AF spins at the EB interface.