Experimental results of investigations of monocrystalline samples ofHg1−x−yCrxMnySesolid solution indicate, first, a considerable influence of manganese atoms introduced inHg1−xCrxSeon the absolute values of physical parameters such as magnetic susceptibility, phase-transition temperature, mobility of conduction electrons, and the period of time during which the samples go over to the equilibrium state, and second, the formation of materials with improved electrophysical and clearly pronounced magnetic characteristics as compared withHg1−xCrxSesamples with the same concentration of chromium ions. ©1998 American Institute of Physics.