Spin-flip effects in the magnetoluminescence and magnetoresistance of semimagnetic narrow-gap Hg1-x-yCdxMnyTe

We report optical and magnetotransport properties in semimagnetic Hg1-x-yCdxMnyTe, a narrow gap semiconductor with an energy gap of about 120 meV. Equivalent phenomena in both optical and magnetotransport measurements of the same set of samples independently indicate selection rules due to the magnetic ions; the photoluminescence (PL) contains optical transitions forbidden by symmetry, and in the longitudinal magnetoresistance a "last" H-0(b) peak forbidden by the conventional selection rules is observed. At T = 5 K, the PL feature related to band-to-band-like transitions shows a well-pronounced splitting in both the Faraday and Voigt geometries, with a subsequent decrease of the higher-energy component for B greater than or equal to 2 T, a behavior which substantially differs from that known for ''nonmagnetic'' Hg1-xCdxTe with a corresponding energy gap. This fundamental difference can be explained in terms of spin relaxation, found to be strongly different for the above-mentioned materials. The results of PL and Shubnikov-de Haas (SdH) measurements are consistently interpreted in terms of a modified Pidgeon-Brown model which includes the s-d exchange interaction between the spin of free carriers and the localized magnetic moments of the Mn2+ ions. The exchange parameters are determined both from the PL and SdH data. Spin-flip transitions caused by exchange coupling is assumed to be responsible for the violation of the particular selection rules.