Electron Paramagnetic Resonance of Exchange-Coupled [Fe⁺–Fe²⁺] Pairs in BaF₂:Fe Crystal

The study of exchange-coupled [Fe⁺–Fe²⁺] pairs that we previously found in X-ray–irradiated BaF₂:Fe crystals was continued by the EPR method. It was confirmed that the ground state of the studied pairs is the electron spin multiplet S = 7/2 split by the anisotropic part of the exchange interaction and by the crystal field so that the ground state turned out to be the Kramers doublet \(\left| { \pm 1{\text{/}}2} \right\rangle \) . It was found that the energy interval to the next spin doublet is 125 GHz. It was established that the nearest ligands of iron ions in the exchange-coupled [Fe⁺–Fe²⁺] pair are eight fluorine ions detected in the EPR spectra as structurally equivalent. The parameters of the superhyperfine interaction with the magnetic moments of the nuclei of these ligand ions were determined. It was shown that the observed experimental facts clearly indicate that the exchange between iron ions in the studied pairs occurs mainly by Zener’s double exchange mechanism.