Superposition Model Analysis of the Spin-Hamiltonian Parameters for Fe³⁺ Ions in Trigonal Symmetry Sites of KMgF₃ and KZnF₃ Single Crystals

A calculation of the trigonal spin-Hamiltonian parameters for Fe 3+ in KZnF 3 was performed using Newman's superposition model and the knowledge of the local arrangement of the fluorine coordinated ligands surrounding the iron ion. It was found that both the sign and the magnitude of the calculated parameters are in good agreement with those previously determined experimentally. Also, an Electron Paramagnetic Resonance (EPR) investigation of Fe 3+ in four inequivalent axial sites (trigonal) of KMgF 3 was carried out and the spin-Hamiltonian parameters describing the site symmetry were determined for the first time. From this information, an analysis was made, using the superposition model, of the local arrangement around the impurity Fe 3+ ion responsible for the observed trigonal EPR spectra.