Fe /Cr interface magnetism: Correlation between hyperfine fields and magnetic moments

Abstract

The magnetic hyperfine field (hff) in epitaxial Fe/Cr(001) superlattices on Mg(001) with different thicknesses of interfacial ${}^{57}\mathrm{Fe}$ probe layers was measured by M\ossbauer spectroscopy. Self-consistent calculations of the Fe and Cr atomic magnetic moments in the interface region were performed within the periodic Anderson model for the same superlattice structure. Different kinds of interface roughness/interdiffusion were modeled using special algorithms. For every kind of interface roughness the distribution of local magnetic moments among the Fe atoms with a given number of nearest and next-nearest Cr neighbors was calculated. We obtain a strong correlation between the experimental hff and calculated local Fe magnetic moments. Peak positions in the hff distribution and correlated positions of maxima in the distribution function for local magnetic moments are observed to be stable relative to changes in the alloylike interface roughness. We found that the hff of \ensuremath{\sim}20 T must correspond to interdiffused Fe atoms inside the Cr spacer layers a few atomic layers away from the ideal interface, contrary to earlier interpretations of Fe atoms at the atomically ``flat'' interface. As a measure of the Fe-Cr interface roughness on an atomic scale our results suggest an enhanced hff in the second Fe layer below the ideal interface in case of atomically smooth interfaces with large flat terraces.