Electron paramagnetic resonance of Ir4+ ions in MgO and CaO

Electron-paramagnetic-resonance spectra of ${\mathrm{Ir}}^{4+}$ were studied in single crystals of MgO and CaO. In each host an isotropic cubic spectrum and two anisotropic tetragonal spectra were observed. Models are proposed for the tetragonal centers, one with a host cation vacancy at a next-nearest-neighbor site to an ${\mathrm{Ir}}^{4+}$ ion in a [100]-type direction, and another including also a cation with a charge greater than 2 at a next-nearest-neighbor site to the vacancy on the defect axis. The tetragonal spectra exhibit quadrupole interaction. The fitting of the spin-Hamiltonian parameters to the EPR spectra was carried out by using a fortran iv version of the MAGNSPEC computer program. The EPR results were used to calculate crystal-field, magnetic, and covalency parameters.