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 (∼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 Δ HC exhibited T temperature dependence expected for noninteracting nanoparticles. The values of blocking temperature TB and HC are found to be maximized for a doping level of 2.5% that corresponds to around five Mn atoms per ZnS nanocrystal.