Hyperfine splitting of Er and Yb resonances in Au: A separation between the atomic and covalent contributions to the exchange integral

The hyperfine splitting has been observed in the magnetic resonance spectrum of dilute Au: Er and Au: Yb alloys. In both cases, the observed hyperfine coupling constant was larger (more positive) than in cubic nonmetallic hosts. Attributing this increase to conduction-electron polarization, and utilizing independent estimates of the 6s contribution to the hyperfine coupling constant, the atomic and covalent contributions to the localized-conduction- electron exchange integral are separated. It is found that the latter increases by an order of magnitude from Er to Yb in Au. This increase is attributed to the nearness of the 4f14 level to the Fermi surface in Au: Yb alloys, noting that Ag: Yb is diamagnetic.