Large increase of magnetic hyperfine fields of5sp-shell impurities in ferromagnets after vacancy trapping

Vacancy trapping by ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sb}$ impurities implanted in Ni, Co, and Fe gives rise to large changes of the magnetic hyperfine fields $B_{\mathrm{hf}}$ of the ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}$ daughter nuclei. We have measured the following values for the normal substitutional and the vacancy-associated impurity hyperfine fields (in T): In all cases, the vacancies associated with the impurities could be "frozen in" up to high temperatures by decoration with post-implanted helium atoms. The substantial increase of the fields can be understood in terms of the conduction-electron polarization model of Blandin and Campbell.