Paramagnetic-Resonance Determination of a Nuclear Quadrupole Interaction by Means of Forbidden Hyperfine Transitions—Ca WO4:Mn2+

Abstract

The $2I$ forbidden hyperfine doublets [$M(\frac{1}{2}\ensuremath{\rightleftarrows}\ensuremath{-}\frac{1}{2})$, $\ensuremath{\Delta}m=\ifmmode\pm\else\textpm\fi{}1$] in the EPR spectrum of ${\mathrm{Mn}}^{2+}$ impurity ions in CaW${\mathrm{O}}_{4}$ have been observed. The doublet separations at $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ are in excellent agreement with a perturbation-theoretic calculation which includes fourth order terms. The angular variation of the separations agrees very well with the angular variation calculated by computer diagonalization of the spin Hamiltonian. The doublet separations for general $\ensuremath{\theta}$ have been computed to order ${(h\ensuremath{\nu})}^{\ensuremath{-}3}$ using perturbation theory and qualitative agreement with the exact angular variation has been obtained. The value obtained for the nuclear quadrupole coupling constant is ${Q}^{\ensuremath{'}}=\ensuremath{-}(0.30\ifmmode\pm\else\textpm\fi{}0.03)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$.