Mossbauer studies of dilute Ag:Fe and Ag:Co alloys

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Abstract
We have studied the dilute Kondo alloys Ag:5 7Fe and Ag:5 7Co via the Mössbauer effect at temperatures between 0.022K and 20K and in applied magnetic fields from 0 to 60 kG. This allows study of both the thermal and magnetic breakup of the non‐magnetic ground state. Our higher temperature results are consistent with those of Kitchens, Steyart 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, HF e h f, 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 5 7Co 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±8) %. The small magnitudes of the hyperfine fields result from the negative core polarization fields being offset by positive orbital fields and illustrate the importance of orbital effects.

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