Optically Induced Changes in the Faraday Rotation Spectra of the Ferromagnetic Semiconductor CdCr2Se4*

Chromium chalcogenide spinel semiconductors have gained attention because of the strong interaction between their electronic and magnetic systems. CdCr2Se4, the most extensively studied Cr spinel, is ferromagnetic and orders at 130 K. The optical absorption edge is found to red shift for temperatures below the Curie point(1). Faraday rotation spectra measured near the absorption edge are highly dispersive with peak rotation increasing and shifting to the red as temperature is reduced. In particular, the rotation spectra scanned at fixed temperature display zero crossings characteristic of the temperature (T less than TC). The red shifting of both the absorption edge as well as the rotation dispersion result from increased magnetic order with reduced temperature(2).