ELECTRONIC ORIGINS OF THE MAGNETIC PHASE-TRANSITIONS IN ZINCBLENDE MN CHALCOGENIDES

Precise first-principles spin-polarized total-energy and band-structure calculations have been performed for the zinc-blende Mn chalcogenides with the use of the local-spin-density (LSD) approach. We find that the LSD is capable of identifying the correct magnetic-ground-state structure, but it overestimates the ordering temperature T(N) and the valence-band exchange splitting DELTA(x)p. The discrepancy is attributed to the overestimation by LSD of the p-d coupling. Adjusting this coupling by an external potential and fitting its parameters to the s- and p-band exchange splitting in MnTe alone, we find that T(N) = 73, 90, and 128 K, respectively, for MnTe, MnSe, and MnS, in good agreement with experiment. This shows that the failures of the LSD in reproducing T(N) and DELTA(x)p share a common physical origin, namely the overestimation of p-d coupling.