Exchange anisotropy and the antiferromagnetic surface order parameter

The temperature dependence of the exchange bias (HE) near the FeF₂ N\'eel temperature (~ 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 (βS~0.8) while samples with smaller grains and smaller height fluctuations have a decreased βS, indicating a more three-dimensional-like phase transition or an increase in the FeF₂ surface exchange interaction.