Indirect superhyperfine interaction in HoVO4(Gd)

Exceptionally large linewidths are observed in the EPR spectra of Gd impurities in the singlet ground-state system HoVO4. A new indirect superhyperfine interaction between the Gd3+ electrons and the Ho3+ nuclei through a highly polarizable Ho3+ electronic state is proposed to account for this behavior. The calculated linewidths are found to be in good agreement with the observations. © 1979 The American Physical Society.