F19 Hyperfine Interaction in the Paramagnetic Resonance Spectrum of Mn++ Ions in ZnF2

Abstract

The observation of a predominantly isotropic fluorine hyperfine interaction in the paramagnetic resonance of ${\mathrm{Mn}}^{++}$ ions dissolved in a Zn${\mathrm{F}}_2$ crystal has been interpreted in terms of the contact interaction of the unpaired $d$ electrons of the ${\mathrm{Mn}}^{++}$ ion at the fluorine nucleus. The distortion produced in the free-ion orbitals of the ${\mathrm{Mn}}^{++}$ $3d$ electrons due to the electrons of the ${\mathrm{F}}^{-}$ ion has been considered. The calculated value of the isotropic hyperfine interaction constant is 10 oersteds, which is about half the experimental value of 19 oersteds. The qudrupole interaction of the ${\mathrm{Mn}}^{++}$ $d$ electrons with the crystalline field gradient, calculated on the point charge model, is found to produce a very small change in the theoretical value. The principal causes which contribute to the quantitative disagreement between the theoretical and the experimental values are also discussed.