EPR Spectra from Ni²⁺ Pairs in KZnF₃ Crystals

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EPR was studied on KNi_xZn_1−xF₃ crystals, where concentration x is less than 0.1. Spectrum from single Ni²⁺ ions was identified by g=2.27, and was superposed by superhyperfine structure from surrounding F⁻ nuclear spins only for the most dilute specimen with x=0.39%. The other line at 8560 gauss observed with K-band microwave was attributed to isolated Ni²⁺ pairs, from the temperature dependence of the intensity. Pair spectra were observed for dilute specimens, and exchange integral J=83 cm⁻¹ was deduced from the temperature dependence of the intensity. In addition, complex superhyperfine structure was observed, and its tentative interpretation was given.