Anomalous Temperature Dependence of the Hyperfine Field at 119Sn Nuclei in Co and Co–Ni Alloys

Abstract

The temperature dependence of the hyperfine field for 119Sn nuclei in Co is anomalous as it decreases much faster with increasing temperature than does the magnetization. For Sn119 in Ni, on the other hand, the hyperfine field-temperature dependence is quite normal. We have performed Mössbauer studies from 4.2°K to the Curie point on alloys of composition Co1−xNix (x=0.4, 0.6, 0.8) that contain 1 at.% 119Sn. The anomalous temperature dependence decreases in a fairly uniform fashion as the composition changes from Co to Ni. A possible explanation of this behavior is that the Sn impurity atom and some fraction of its nearest neighbors may act as a spin polarized unit which behaves like a localized moment in the ferromagnetic host. If one assumes that, the anomalous temperature dependence can be explained by a molecular field model.