Effect of anisotropy on the critical antiferromagnet thickness in exchange-biased bilayers

TLDR

The two fluoride systems share identical crystal structures and lattice constants, but their anisotropy fields differ by a factor of 20. The study aims to directly establish how antiferromagnet anisotropy influences the thickness dependence of exchange bias by comparing FeF₂/Fe and MnF₂/Fe bilayers. The authors measured exchange bias versus antiferromagnet thickness in both bilayers, and examined temperature dependence and structural morphology to rule out blocking‑temperature or discontinuity effects. The critical antiferromagnet thickness for exchange bias onset is an order of magnitude smaller in the more anisotropic fluoride, confirming that anisotropy governs the critical thickness.

Abstract

The dependence of exchange bias on antiferromagnet thickness has been measured in ${\mathrm{FeF}}_{2}/\mathrm{Fe}$ and ${\mathrm{MnF}}_{2}/\mathrm{Fe}$ bilayers. The two fluoride systems have identical crystal structures, similar lattice constants, but anisotropy fields that differ by a factor of 20. Hence, by comparing the antiferromagnetic layer thickness dependence of the exchange bias in the two systems we are able to directly establish the effect of the antiferromagnet anisotropy. We find that the critical antiferromagnet thickness for the onset of exchange biasing is an order of magnitude smaller for the more anisotropic fluoride, confirming the often-used assumption that the anisotropy dictates the critical thickness. By measuring the temperature dependence of the exchange bias and the structural morphology of the layers we are able to prove that the effects we observe are not due to the blocking-temperature thickness dependence or the onset of discontinuity in thin antiferromagnet layers.