Exchange anisotropy and the antiferromagnetic surface order parameter

The temperature dependence of the exchange bias (H-E) near the FeF2 Neel temperature (similar to 78.4 K) was correlated with structural measurements in FeF2-Fe bilayers. Low-angle x-ray diffraction and atomic force microscopy show that samples with larger height fluctuations have larger lateral grain sizes. Samples with larger lateral grain sizes exhibit a surface critical exponent (beta(S) similar to 0.8) while samples with smaller grains and smaller height fluctuations have a decreased beta(S), indicating a more three-dimensional-like :il-like phase transition or an increase in the FeF2 surface exchange interaction.