Investigations of ESR superhyperfine structure for the cubic Gd3+ center in CaF2, SrF2, and BaF2

A partially resolved superhyperfine structure has been observed in the ESR spectra of the cubic Gd³⁺ center in CaF₂, SrF₂, and BaF₂. This superhyperfine structure has been satisfactorily analyzed in terms of the interaction of the Gd³⁺ ion with its eight nearest‐neighbor ¹⁹F nuclear spins associated with the cubic Gd³⁺ center. The values of the fluorine superhyperfine interaction constants T_∥ and $T_{\perp }$ obtained by this analysis are (in units of MHz): T_∥=7.5±0.2, $T_{\perp }\text{=−6.7± 0.2}$ for SrF₂; T_∥=8.0±0.3, $T_{\perp }\text{=−5.9± 0.3}$ for BaF₂; and T_∥=8.1±0.2, $T_{\perp }\text{=−7.1± 0.2}$ for CaF₂ (which agree with those determined previously by ENDOR).