Onset of exchange bias in ultrathin antiferromagnetic layers

TLDR

Exchange bias is traditionally attributed to magnetic domains in the antiferromagnetic layer, with both planar and perpendicular domain wall models proposed to explain observed effects. The study investigates how exchange bias depends on antiferromagnetic layer thickness in IrMn/Co and FeMn/Co bilayers. The authors measured exchange bias versus AF layer thickness in IrMn/Co and FeMn/Co systems. Bias onset occurs at AF thicknesses (~10 Å) too thin for planar domain walls, implying perpendicular domain walls are the likely mechanism.

Abstract

Current theoretical explanations of exchange biasing are based upon magnetic domains in the antiferromagnetic layer being responsible for the phenomenon. Both the ideas of planar and perpendicular domain walls have been developed in explaining the various observed effects. Here the exchange bias ${(H}_{\mathrm{ex}})$ has been investigated as a function of the antiferromagnetic (AF) layer thickness ${(t}_{\mathrm{AF}})$ in IrMn/Co and FeMn/Co exchange biased systems. The results indicate that the onset of biasing occurs for ${t}_{\mathrm{AF}}$ which appears to be far too low $(\ensuremath{\sim}10\mathrm{\AA{}})$ to accommodate planar domain walls $(\ensuremath{\sim}200\mathrm{\AA{}})$ within the AF layer. From these results it is inferred that planar domain walls cannot therefore be responsible for biasing, and that theoretical calculations involving perpendicular domain walls in the antiferromagnetic layers appear to be the more plausible explanation.