Superposition-model analysis of the second- and fourth-order spin-Hamiltonian parameters of Fe3+ in the fluoroperovskite compounds. A new EPR study of Fe3+ in KMgF3

Abstract

A new study of the strong axial EPR spectra of ${\mathrm{Fe}}^{3+}$ in KMg${\mathrm{F}}_3$ is presented. In addition to the previously reported spin-Hamiltonian parameters $g_{\parallel }$, $g_{\perp }$, and $b_2^0$ for this axial site, values for the crystal-field parameters $b_4^0$ and $b_4^4$ are determined for the first time. Forbidden transitions of the type $\Delta M_s=\pm 2 \mathrm{and} \pm 3$, previously unreported, are observed in the EPR spectra. The applicability of the superposition model to the second- and fourth-order spin-Hamiltonian parameters for the strong axial site of ${\mathrm{Fe}}^{3+}$ in the fluoroperovskite compounds KMg${\mathrm{F}}_3$, KZn${\mathrm{F}}_3$, and RbCd${\mathrm{F}}_3$ is analyzed. It is established that the experimental reported values for the $b_2^0$ parameter can be fitted if the intrinsic parameter ${\overline{b}}_2^{\mathrm{F}}$ of the fluorine ion is -0.09 ± 0.03 ${\mathrm{cm}}^{-1\mathrm{}}$ and the power-law coefficent $t_2$ of ${\overline{b}}_2^{\mathrm{F}}$ is taken to be equal to 12 ± 2. On the other hand, it is found that in order to get a consistent model for the FeO${\mathrm{F}}_5$ cluster center, responsible for the observed strong axial EPR spectra of ${\mathrm{Fe}}^{3+}$ in the fluoroperovskite compounds, the sign of both spin-Hamiltonian parameters $b_4^0$ and $b_4^4$ must be positive and opposite to that of $b_2^0$. Values for the intrinsic parameter ${\overline{b}}_4^{\mathrm{F}}$ of the fluorine ion and for the power-law coefficient $t_4$ of ${\overline{b}}_4^{\mathrm{F}}$ are also determined.