Temperature dependence of hyperfine magnetic fields in Fe-Co alloys

A Mössbauer spectrometry study of bcc Fe-Co alloys was performed to measure the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ hyperfine-field parameters from 77 to 900 K. The temperature dependence of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ hyperfine magnetic field in Fe-Co alloys was similar, although not identical, to that of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in pure Fe. These results are understood if the alignment of magnetic moments at Fe atoms is only slightly more temperature dependent than at Co atoms. This situation for Fe-Co is significantly different from that of Fe-Ni alloys, indicating that the interatomic exchange interactions in Fe-Co alloys are stronger than in Fe-Ni.