Investigation of dilute magnetic impurities via the Mössbauer effect:AgFe57andAgCo57

We have studied the dilute Kondo alloys $\mathrm{Ag}{}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ and $\mathrm{Ag}{}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ via the Mössbauer effect at temperatures between 0.022 and 4.2 K and in applied magnetic fields from 0 to 60 kG. For Fe in Ag, this allows study of both the thermal and magnetic breakup of the nonmagnetic ground state. Where they overlap, our results agree with those of Kitchens, Steyert, and Taylor. As the temperature is lowered, a strong reduction from free spin behavior of the local moment is observed. At our lowest temperatures the dependence of the Fe-hyperfine field on applied field is compared with several theoretical and semiempirical expressions, where each describes the data moderately well, none with marked superiority. We also report the first measurements of the hyperfine field of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ in Ag, obtained via the intensity asymmetry of the spectra. The field can be described in terms of a large positive Knight shift $K=(28\mathrm{}\pm 8)\%$.