Paramagnetic Resonance ofHo3+in a Trigonal Site in SrF2

A paramagnetic-resonance spectrum of ${\mathrm{Ho}}^{3+}$ in a trigonal site in Sr${\mathrm{F}}_2$ was observed. The spectrum is characteristic of a non-Kramers ion, and the asymmetric line shape indicates that the non-Kramers ground doublet requires low-symmetry strain distortions to split the doublet and observe paramagnetic-resonance transitions of the magnetic dipole type. The spectrum is interpreted in terms of a standard spin Hamiltonian for a non-Kramers doublet with the parameters $g_{\parallel }=18.2\mathrm{}\pm 0.1$, ${\Delta }_0=0.033\mathrm{}\pm 0.001$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\mathrm{}\left|A\right|=0.397\mathrm{}\pm 0.005$ ${\mathrm{cm}}^{-1\mathrm{}}$. The possibility of observing paraelectric resonance in this site, which lacks inversion symmetry, was investigated. A discussion of various possible eigenfunctions, transitions, and line shapes in crystal fields of threefold and fourfold symmetry is given.