Localized Polarization on Sn Atoms in Ferromagnetic Transition Metals and Alloys

We have made 119Sn Mössbauer measurements on an alloy of Fe0.5Ni0.5 containing 1 a/o 119Sn from 4.2 K to the Curie point. 57Fe Mössbauer measurements were also made from 4.2 to 300 K. The hyperfine field at 119Sn nuclei behaves anomalously, decreasing much faster with temperature than does the magnetization, in a manner similar to that observed in Co. We interpret this anomalous behavior as being caused by a localized polarization associated with the Sn impurity and are able to fit the field-vs-temperature data well with a localized moment molecular field theory. A model of the Anderson type is outlined which indicates how localized polarization can form on a ``nonmagnetic'' impurity.