Dynamical interactions in EuAsO4(Gd) and EuVO4(Gd)

Electron-paramagnetic-resonance experiments on ${\mathrm{Gd}}^{3+}$ impurities in the singlet-ground-state zircon systems EuAs${\mathrm{O}}_4$ and EuV${\mathrm{O}}_4$ have been used to study the various possible dynamical interactions in these systems. The low-lying degenerate excited states of ${\mathrm{Eu}}^{3+}$ in these compounds can produce dynamical electric, magnetic, and exchange fields in the lattice. From the ratios of the linewidths in the fine-structure spectra of EuAs${\mathrm{O}}_4$(Gd) and EuV${\mathrm{O}}_4$(Gd), we find that the dynamical magnetic and/or exchange fields are dominant over the dynamical electric fields caused by the Jahn-Teller effect. From the relative magnitudes of the linewidths in the two compounds, we conclude that exchange interactions are more important than the magnetic dipolar effects.