Hyperfine Fields in Fe-Si Alloys

Abstract

We have measured the hyperfine field at Fe and Si nuclei in Fe-Si alloys containing 18.4 to 26.5 at. % Si by the NMR spin-echo technique at 4.2°K. We observe Fe resonances from nuclei at sites with 3, 4, 5, 6, and 8 Fe nearest neighbors at frequencies which are in good agreement with the reported Mössbauer results. In Fe3Si, we observe an additional line at about 31.5 Mc/sec which we identify with the Si nuclei. In the 23.0 at. % sample, this line is diminished in intensity and another line appears at about 47 Mc/sec which grows in intensity as the Si concentration is decreased below 23.0 at. %. At 22.3 at. % Si and below, the 31.5-Mc/sec Si line is not observed. In addition, our data shows that a significant change in the Fe hyperfine field at sites with 4 and 8 nearest-neighbor Fe atoms occurs between 22 and 24 at. % Si. These observations on the hyperfine fields correlate well with the anomalous behavior of the resistivity in this concentration range and indicate a change in the electronic structure of Fe-Si alloys that occurs in the vicinity of 23 at. % Si.