A MODIFIED PHENOMENOLOGICAL DESCRIPTION OF THE EXCHANGE INTERACTIONS IN DILUTE MAGNETIC SEMICONDUCTORS

Magnetoreflectivity spectroscopy has been conducted on a series of Cd- 1-x,MnxTe epilayers (x < 0.2) in magnetic fields up to 45 T. For Mn co ncentrations greater than a fraction of one per cent, the electronic s p-d exchange interactions do not saturate for B > 10 T at 4.2 K, as pr edicted by the widely used mean spin model of Gaj et al [1], but conti nue to increase with increasing magnetic field. This is because of a f ield-dependent increase in the total resultant spin of the dilute magn etic sublattice, due to a reduction in the antiferromagnetic interacti ons between the Mn2+ ions. We present a modified phenomenological desc ription of the exchange interactions, which simply and efficiently acc ounts for this field-induced increase in spin, necessary for an accura te description of the high-field (B > 10 T) regime. This is achieved s emi-empirically within the mean spin formalism, without requiring solu tion of the complex spin Hamiltonians for double, triple and higher or der clusters.