Spin waves in diluted magnetic quantum wells

We study collective spin excitations in two-dimensional diluted magnetic semiconductors, placed into external magnetic field. Two coupled modes of the spin waves (the electron and ion modes) are found to exist in the system along with a number of the ion spin excitations decoupled from the electron system. We calculate analytically the spectrum of the waves taking into account the exchange interaction of itinerant electrons both with each other and with electrons localized on the magnetic ions. The interplay of these interactions leads to a number of intriguing phenomena including tunable anticrossing of the modes and a field-induced change in a sign of the group velocity of the ion mode.