Electronic Properties of ${\mathrm{Fe}}^{2+}$ in Cubic KMg${\mathrm{F}}_3$ from Mössbauer Spectroscopy

Iron-doped KMg${\mathrm{F}}_3$ single crystals have been studied by Mössbauer spectroscopy of ${\mathrm{Fe}}^{57}$. Single lines due to ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ are observed at room temperature. For $T<\mathrm{}12\mathrm{}$ K, the ${\mathrm{Fe}}^{2+}$ line splits into a quadrupole doublet with a splitting $\Delta E_Q=0.\mathrm{}44\pm 0.02$ mm/sec. Comparison with a random-strain model due to Ham yields a value of 120 ${\mathrm{cm}}^{-1\mathrm{}}$ for the position of the first excited spin-orbit split level. Magnetic hyperfine structure in external magnetic fields at low temperature is observed and analysis yields a value of -495 ±30 kOe for the corepolarization hyperfine field in ${\mathrm{Fe}}^{2+}$ and a value of 4.1 a.u. for $〈\frac{1}{r^3}〉$.