SPIN-FLIP EFFECTS IN THE MAGNETOLUMINESCENCE AND MAGNETORESISTANCE OFSEMIMAGNETIC 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 12 0 meV. Equivalent phenomena in both optical and magnetotransport measu rements of the same set of samples independently indicate selection ru les due to the magnetic ions; the photoluminescence (PL) contains opti cal transitions forbidden by symmetry, and in the longitudinal magneto resistance a ''last'' H-0(b) peak forbidden by the conventional select ion rules is observed. At T = 5 K, the PL feature related to band-to-b and-like transitions shows a well-pronounced splitting in both the Far aday and Voigt geometries, with a subsequent decrease of the higher-en ergy component for B greater than or equal to 2 T, a behavior which su bstantially differs from that known for ''nonmagnetic'' Hg1-xCdxTe wit h a corresponding energy gap. This fundamental difference can be expla ined in terms of spin relaxation, found to be strongly different for t he 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 betwe en the spin of free carriers and the localized magnetic moments of the Mn2+ ions. The exchange parameters are determined both from the PL an d SdH data. Spin-flip transitions caused by exchange coupling is assum ed to be responsible for the violation of the particular selection rul es.