Collective excitations in a magnetically doped quantized Hall ferromagnet

A theory of collective states in a magnetically quantized two-dimensional electron gas (2DEG) with half-filled Landau level (quantized Hall ferromagnet) in the presence of magnetic 3d impurities is developed. The spectrum of bound and delocalized spin excitons as well as the renormalization of Zeeman splitting of the impurity 3d levels due to the indirect exchange interaction with the 2DEG are studied for the specific case of n -type GaAs doped with Mn, where the Landé g factors of impurity and 2DEG have opposite signs. If the sign of the 2DEG g factor is changed due to external influences, then impurity related transitions to new ground state phases, presenting various spin-flip and skyrmionlike textures, are possible. Conditions for the existence of these phases are discussed.