Electron spin resonance linewidths of Fe3+ in magnesium oxide

Abstract

Electron spin resonance linewidths of Fe3+ in single crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Fe3+ concentration. In contrast to the behaviour expected from dipolar broadening the experimental derivative peak-to-peak linewidth for the 1/2 ↔ −1/2 transition, about 0.6 mT at 77 K and a polar angle of 0°, was independent of concentration from 140 to 8500 ppm. The calculated dipolar linewidths greatly exceeded those observed and values of the ratio of moments M41/4/M21/2derived from the experimental data lay between 1.33 and 1.48. Optical examination, coupled with heat-treatment experiments, confirmed that the predominant valency state present was Fe3+. The data suggested that Fe3+ entered the lattice substitutionally, occupying magnesium sites, and that the linewidths were determined by exchange narrowing over the whole concentration range examined.