DIMENSIONAL DEPENDENCE OF ANTIFERROMAGNETISM IN DILUTED MAGNETIC SEMICONDUCTOR HETEROSTRUCTURES

We have performed magneto-optical studies on a series of thin CdTe/(CdMn)Te single quantum wells at low temperatures and in external magnetic fields up to 7.5 T. As a consequence of the high manganese content of the barrier layers (x > 20%) the antiferromagnetic exchange interaction between the manganese spins exhibit spin-glass behaviour. By comparison of the Zeeman splitting of barrier and quantum well excitons, we found a reduced antiferromagnetic coupling of Mn-spins near the heterointerface. We assume that the missing of nearest-neighbour manganese spins adjacent to the transition from magnetic to nonmagnetic materials results in a reduced probability of finding antiferromagnetically coupled Mn-Mn clusters. The mechanism of interface-related frustrated antiferromagnetism leads to the astonishing result of comparable or even larger Zeeman splittings of quantum well excitons compared with those observed in barrier layers. If we introduce a second interface for the magnetic layer as can be realized with ultrathin superlattices, missing nearest neighbours produce a more pronounced frustration of antiferromagnetic coupling due to the quasi two-dimensional character of the magnetic layer, which is correlated with a higher percolation threshold.