OPTICAL AND MAGNETIC-PROPERTIES OF FE2-VI SEMICONDUCTORS - THE JAHN-TELLER EFFECT( AND CR2+ IN II)

The D-5 terms of Fe2+ and Cr2+ in the tetrahedral potential at cation sites in II-VI compounds split into orbital doublet and triplet states . While in Cr2+ the orbital tripler has lower energy than the doublet the opposite is the case in Fe2+. Both ions have singlet ground states after the spin-orbit interaction is taken into account and, hence, bo th are Van Vleck paramagnets. The optical absorption spectra of Fe and Cr based materials differ and are explained on the basis of a dynamic Jahn-Teller effect in the former and a static one in the latter. Thes e considerations permit us to explain the optical as well as the magne tic properties observed in these materials.