Anticrossing of Raman lines in Cd1−xFexSe: Van Vleck–type bound magnetic polaron

Abstract

Anticrossing of two Raman lines, that of a donor-electron spin flip and that of an intra-${\mathrm{Fe}}^{++}$-ion excitation, has been observed in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Fe}}_{\mathrm{x}}$Se, a Van Vleck–type semimagnetic semiconductor. A new model of a bound magnetic polaron (BMP) is reported, which accounts for the experimental data. At zero magnetic field, this BMP is characterized by a finite local spin polarization at its center, 〈${\mathrm{S}}^{\mathrm{x}}$〉=0.06, and by an exchange energy shift of its ground state of Δ${\mathrm{E}}_{\mathrm{p}}$=-0.26 ${\mathrm{cm}}^{\mathrm{-}1}$ for x=0.018, despite the fact that the spin-flip energy of the donor electron is strictly zero.