Effect of in doping on the giant faraday rotation of Cd_0.8Mn_0.2Te crystal

Faraday rotation and near infrared transmission properties of Cd_0.8Mn_0.2Te wafers and those with different In doping concentration in the range from 10¹⁶ to 10¹⁹ atoms/cm³ were studied at room temperature. It was showed that with the increase of the photon energy, the Verdet constants of Cd_0.8Mn_0.2Te and Cd_0.8Mn_0.2Te: In were increased. Moreover, the Verdet constant of Cd_0.8Mn_0.2Te depended on In doping concentration. In the un-doped Cd_0.8Mn_0.2Te crystal, the Verdet constant was measured to be 710-1820(°)/cm·T in the photon energy range of 1.63-1.72 eV. When 8.96×10¹⁶ atoms/cm³ In was doped, the Verdet constant was increased to 720-1960(°)/cm·T. However, the values was decreased to 660-1630, 490-1090(°)/cm·T when In doping concentration reached 2.39×l0¹⁷and 4.48×10¹⁸ atoms/cm³ respectively. When 2.99×10¹⁹atoms/cm³ In was doped, the Verdet constant was decreased to 460-740(°)/cm·T in the photon energy range of 1.63-1.70 eV. For low In concentration, the increase of the Verdet constant was a result of the increase of valence-band electrons, leading to an enhancement of exchange interaction between p-like valance-band electrons and 3d electrons of Mn²⁺. On the contrary, for high In concentration, the effects of the exchange interaction between s-like conduction-band electrons and 3d electrons of Mn²⁺ were enhanced, leading to the further decrease of the spin-split conduction-band and the decrease of the Verdet constant.