The migration of Mn2+ ions in Cd1−xMnxS nanocrystals: Thermal annealing control

This work reports evidence of the induced migration of Mn2+ ions in Cd(1−x)MnxS nanocrystals (NCs) by selecting a specific thermal treatment for each sample. The growth and characterization of these magnetic dots were investigated by atomic force microscopy (AFM), optical absorption (OA), and electronic paramagnetic resonance (EPR) techniques. The comparison of experimental and simulated EPR spectra confirms the incorporation of Mn2+ ions both in the core and at the dot surface regions. The thermal treatment of a magnetic sample, via selected annealing temperature and/or time, affects the fine and hyperfine interaction constants which modify the shape and the intensity of the EPR transition spectrum. The identification of these changes has allowed tracing the magnetic ion migration from core to surface regions of a dot as well as inferring the local density of the magnetic impurity ions.

► We trace the migration process of magnetic ions in single-phase nanocrystals.
► The migration from the crystal core to the surface depends on the thermal treatment.
► Combined EPR and optical absorption thoroughly characterize this process.