Birefringence and Faraday effect in Cd1-xMnxSe.

Abstract

We have studied the birefringence and the Faraday effect in the uniaxial diluted magnetic semiconductor (DMS) ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se with k\ensuremath{\perp}c^, where k is the direction of propagation of the light and c^ the optic axis. The birefringence in the absence of an external magnetic field was determined from the channeled spectrum of light transmitted by a wedged sample. The birefrigence increases slightly with increasing photon energy well below the absorption edge, but decreases sharply as the photon energy approaches it. The temperature dependence of the birefringence is dominated by the temperature dependence of the band gap. The birefringence depends on the manganese concentration (x); it increases with x as does the ratio of the lattice parameters (c/a). With an external magnetic field H?k\ensuremath{\perp}c^, the polarizations that travel inside the medium without change of form are two elliptical vibrations rotating in opposite directions having their major axes parallel and perpendicular to c^, respectively. Close to the absorption edge, the phase difference between these two vibrations, \ensuremath{\Delta}, rapidly increases with the increasing external magnetic field due to the giant Faraday rotation in DMS alloys. Using the Poincar\'e sphere construction, \ensuremath{\Delta} is separated into birefringence and Faraday-rotation contributions. The Faraday rotation in this configuration shows saturation effects at low temperatures and high magnetic fields following the same behavior as the magnetization of ${\mathrm{Mn}}^{2+}$. The functional form of photon-energy dependence of the Verdet constant (V) is very similar for H\ensuremath{\perp}c^ and H?c^, although V for the former is smaller. Our studies point to the more significant role of the B exciton in the H?k\ensuremath{\perp}c^ configuration, probably due to the larger Zeeman splitting of the B exciton.