Mg25superhyperfine structure ofV-type defects in MgO

We report electron-nuclear double-resonance measurements of the magnetic hyperfine and electric quadrupole interactions of the ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$ neighbors of the $V^{-}$ center in MgO for both the single-axial neighbor and the four equatorial neighbors of the trapped hole. Parameters have also been determined for the single-axial neighbor in a series of six $V$-type centers ranging from the $V^{-}$ (charge uncompensated) to ${\mathrm{}\left[\mathrm{Na}\right]\mathrm{}}^0$ (nearby-charge compensation). The results for the single-axial neighbor exhibit a systematic variation of both the negative contact and the electric quadrupole interactions with the distance of the charge compensator from the hole. The interactions between the equatorial neighbors and the trapped hole of the $V^{-}$ center imply a slight axial displacement of the trapped hole out of the plane of equatorial neighbors. A reasonable choice of absolute signs for the magnetic interaction gives a negative contact interaction, implying exchange core polarization is dominant for the equatorial neighbors. Evidence is presented to show that the magnetic interaction between the trapped hole and the equatorial neighbors is essentially unaffected by the various charge compensators.