Characterization of ferrous ions in hafnium-doped yttrium iron garnet

Abstract
The ferrous content of hafnium-doped yttrium iron garnet crystals has been determined by a number of methods and microwave measurements of the temperature dependence of the anisotropy constant found to give the most reliable value. The Fe2+ ions have a doublet energy level lying lowest with a maximum splitting of 75 cm-1.