Tuning magnetic disorder in diluted magnetic semiconductors using high fields to 89 tesla

We describe recent and ongoing studies at the National High Magnetic Field Laboratory at Los Alamos using the new "100 Tesla Multi-Shot Magnet", which is presently delivering fields up to ∼89 T during its commissioning. We discuss the first experiments performed in this magnet system, wherein the linewidth of low-temperature photoluminescence spectra was used to directly reveal the degree of magnetic alloy disorder 'seen' by excitons in single Zn_0.80Cd_0.22Mn_0.08Se quantum wells. The magnetic potential landscape in II-VI diluted magnetic semiconductors (DMS) is typically smoothed when the embedded Mn²⁺ spins align in an applied field. However, an important (but heretofore untested) prediction of current models of compositional disorder is that magnetic alloy fluctuations in many DMS compounds should increase again in very large magnetic fields approaching 100 T. We observed precisely this increase above ∼70 T, in agreement with a simple model of magnetic alloy disorder.