Photoinduced infra‐red optical absorption in CdCr₂Se₄ magnetic semconductor

Abstract

Magnetic semiconductors exhibit many interesting effects due to mutual interrelations of electric, optical, and magnetic properties. A few photoinduced effects in the magnetic semiconductor CdCr Se have been reported so far: photoconductivity /1 to 3 / , change of the high frequency magnetic permeability under illumination /4 to 6 / , change of magnetic hysteresis loops /7/, effect of light on the ferromagnetic resonance and on magnetostatic modes, and finally change of the spectral dependence of photoconductivity under additional illumination /8/. These effects a r e induced by photons with energies in the region of the absorption edge, more precisely in the region of the absorption band which emerges from the absorption edge with increasing magnetic ordering of the sample /9/. This "red shiftingv7 absorption band reveals pronounced polarization properties / l o / . This short note deals with the optical absorption structures within the spectral range 0 . 1 to 1 . 1 eV induced by an additional illumination with photon energies in the region of the mentioned "red shifting" band. 4Single crystals of CdCr Se were grown from the melt of anhydrous CdC12 and 2 4 they were found to be compensated p-type samples. The specimens for measurements were prepared in the form of plates with thicknesses 0 . 1 to 0 . 5 mm by grinding and mechanical polishing.The optical absorption measurements were .performed with a Carl Zeiss SPM 2 monochromator with LiF and NaCl prisms in the respective spectral regions. The excitation spectra were measured by another SPM 2 monochromator with a glass prism. The circular polarization of beams in the region of photon energies 0 . 4 t o 1 . 4 eV was obtained by a polarizer coupled with a calibrated Babinet-Soleil compensator. The beam used for absorption measurements ("probing beam") was commonly chopped at the frequency 290 Hz in the spectral range 0 . 4 to 1 . 2 eV (PbS photodetector). Only measurements of the dependence of the excitation spectra on the