EPR and electron-nuclear-double-resonance investigations ofFe3+in KMgF3

Single crystals of iron-doped KMg${\mathrm{F}}_3$ show a strong axial EPR spectrum with partially resolved hyperfine structure. The spectrum arises from ${\mathrm{Fe}}^{3+}$ in a crystalline field of [100] axial symmetry. An electron-nuclear-double-resonance study of the hyperfine interaction gives positive support to the model previously proposed. The iron ion substitutes for a magnesium ion, and one of the surrounding six-nearest-neighbor fluorine ions is either missing or replaced by a charge-compensating impurity such as ${\mathrm{O}}^{--}$, thus giving rise to an axial distortion. The measured values for the spin-Hamiltonian parameters are $D=0.352\mathrm{}\pm 0.005$ ${\mathrm{cm}}^{-1\mathrm{}}$, $g_{\parallel }=2.0042\mathrm{}\pm 0.0005$, and $g_{\perp }=2.0120\mathrm{}\pm 0.0005$, where $g$ is axially symmetric about the symmetric axis of the crystalline-field parameter $D$. The nearest-neighbor hyperfine interaction constants are $\frac{A_{\parallel }}{h}=104.6\mathrm{}\pm 0.1$ MHz and $\frac{A_{\perp }}{h}=55.7\mathrm{}\pm 0.1$ MHz for the four ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ ions in a (100) plane perpendicular to the symmetry axis of $D$, and $\frac{A_{\parallel }}{h}=43.2\mathrm{}\pm 0.5$ MHz, $\frac{A_{\perp }}{h}=24.6\mathrm{}\pm 0.1$ MHz for the single ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ ion along the symmetry axis of $D$. It is assumed that the hyperfine interaction tensors are axially symmetric about their corresponding Fe-F bond directions.