Achieving Ferromagnetism in Single-Crystalline ZnS Wurtzite Nanowires via Chromium Doping

The magnetic properties of Cr-doped wurtzite ZnS nanowires were studied through first-principles computations. At a low doping concentration of 2.08% (one Cr atom in a 96-atom supercell), the Cr atom prefers to substitute for the surface four-coordinated Zn atom in the groove of the ZnS nanowire with a diameter of 1.2 nm; at a higher doping concentration of 4.17% (two Cr atoms in the 96-atom supercell), the Cr atoms preferably substitute for the surface four-coordinated Zn atom and its neighboring surface three-coordinated Zn atom. Irrespective of the sites that Cr atoms occupy, Cr atoms in ZnS nanowires are always ferromagnetically coupled to each other and antiferromagnetically coupled to the mediating S atom; moreover, the robust ferromagnetism is not sensitive to surface passivation. The ferromagnetism in Cr-doped ZnS nanowires is attributed to a double-exchange mechanism.