High-magnetic-field EPR of Cr-based diluted magnetic semiconductors

We have studied magnetic interactions in chromium-based diluted magnetic semiconductors by measuring in detail the electron paramagnetic resonance spectrum of ${\mathrm{Cr}}^{2+}$ over the frequency range between 30 and 210 GHz at high magnetic fields up to 20 T oriented along different crystal axes. At low temperatures, crystals of chromium-alloyed zinc chalcogenides ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}$ (S, Se, Te) demonstrate complex properties that are neither of Brillouin nor of Van Vleck type. The behavior of these ${\mathrm{Cr}}^{2+}$ impurities in semimagnetic materials results from the interaction of the ground state with the low-lying electronic states of the $3d{\mathrm{Cr}}^{2+}$ ion and from the Jahn-Teller-induced distortion of the ${\mathrm{Cr}}^{2+}$ position in the host lattice. We measured optical transitions between these states and we could determine the magnetic-field dependence and the anisotropy of the electronic levels. We explain our results with the crystal-field model proposed by Vallin et al.,1 including a cubic crystal field and Jahn-Teller distortion, and we evaluate the dependence of the model parameters on the semiconductor host lattice.