Temperature dependence of hyperfine fields at rare-earth nuclei in iron and nickel

The temperature dependence of the hyperfine fields [$H_0\mathrm{}\left(T\right)\mathrm{}$] at ${}_{}{}^{146}{}_{}{}^{}\mathrm{Nd}$ and ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$ nuclei recoil implanted into polarized Fe and Ni were measured from 4 to 650 K with the ion-implantation perturbed-angular-correlation technique. Experimental results for $H_0\mathrm{}\left(4\right)\mathrm{}$ are: FeNd, 3.04(71) MOe; NiNd, 1.67(39) MOe; FeSm, 3.14(35) MOe; NiSm, 1.77(17) MOe. The hyperfine magnetic fields induced at the implanted nuclei by the unquenched orbital angular momentum of the partially filled ionic $4f$ shell [$H_{4f}\mathrm{}\left(T\right)\mathrm{}$] were deduced and the results analyzed in terms of the interactions of the respective rare-earth ionic states with the internal fields of the hosts. Interaction models incorporating pure exchange interactions, exchange and crystal electric field interactions, various implant final-site symmetries, and ionic-excited-state mixing were least-square fit to $H_{4f}\mathrm{}\left(T\right)\mathrm{}$ over various intervals of the observed temperature range. Crystal-electric-field effects are shown to be important in all cases except, perhaps, FeSm. The results of each least-squares-fit analysis are presented and discussed.