Temperature Anomalies of Hyperfine Fields ofs−pImpurity Elements in Cobalt

The hyperfine magnetic field $H_{\mathrm{hf}}$ at extremely dilute impurities of Ga, Ge, and As in a single crystal of hcp Co has been measured as a function of the temperature $T$ up to $T\cong 900°$ K. The functions $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$ exhibit dramatic differences for these adjoining elements; while $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$ in $\mathrm{As}\mathrm{Co}$ scales with the hcp host magnetization $\sigma \mathrm{}\left(T\right)\mathrm{}$, $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$ in $\mathrm{Ga}\mathrm{Co}$ decreases much faster than $\sigma \mathrm{}\left(T\right)\mathrm{}$ and $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$ in $\mathrm{Ge}\mathrm{Co}$ increases by ∼25%. This is the first observation of an increase with temperature of the magnitude of the hyperfine field at an impurity atom in any ferromagnetic metal.