Ferromagnetism in zinc sulfide nanocrystals: Dependence on manganese concentration

Ferromagnetic ordering in nanocrystallites of dilute magnetic semiconductors arises due to a fascinating interplay of carrier concentration, randomness of magnetic impurity sites, and size-induced quantum confinement. We here report results of a magnetization study on ZnS nanoparticles (similar to 2.5 nm) carried out by varying the doping concentration of substitutional Mn ions that occupy cationic sites without altering the carrier concentration. Ferromagnetic ordering and giant Zeeman splitting are observed below 30 K in these nanoparticles for doping above 1.5%. The change in coercive field Delta H-C exhibited root T temperature dependence expected for noninteracting nanoparticles. The values of blocking temperature T-B and H-C are found to be maximized for a doping level of 2.5% that corresponds to around five Mn atoms per ZnS nanocrystal.