Onset of exchange bias in ultrathin antiferromagnetic layers

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_ex) has been investigated as a function of the antiferromagnetic (AF) layer thickness (t_AF) in IrMn/Co and FeMn/Co exchange biased systems. The results indicate that the onset of biasing occurs for t_AF which appears to be far too low (∼10Å) to accommodate planar domain walls (∼200Å) 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.