Carbon Mediated Magnetic In Co-Doped ZnS

ZnS doping with transition metal(TM) has the properties of both semiconductor and magnetic materials. It can utilize the freedoms of electron charge and spin at the same time. It makes a great contribution to luminesce and magnetic storage. The bulk ZnS in room temperature has a direct band gap, 3.72 eV, the bound energy of exciton is 38 meV,larger than the thermal activation energy(26 meV). TM doped ZnS has the potential to become the materials with better magnetic and optical properties. We use the first principle method based on Density Functional Theory to study the magnetic and optical properties of Co doped ZnS and modulation of C, N to Co-doped ZnS. We also calculate the magnetic and optical properties of Co/Mn co-doping. The following results are obtained:(1) The magnetic and optical properties of Co doped ZnS was calculated. The results shows that the total energy of AFM is lower than that of FM, which indicates the AFM state is more stable. When the two Co2+ are connected with the same S2-, the total energy is the lowest. We also calculate the crystal splitting energy and spin exchange splitting energy. From the imaginary of dielectric function, we know that absorption peak begins at 0.7 eV,that means the optical band gap of ZnS:Co is 0.7 eV.(2) The effect of C on the magnetic order in the system of ZnS:Co is studied. The FM order is much stable than AFM order. No matter the direction of initial magnetic moment is parallel or untiparallel, it turns in opposite. The total magnetic moments are 1 μB for one C and one Co co-doped ZnS. That means C always couples with the neghbor Co in AFM order. Therefore in the sysmtem with two Co couple in FM order. The total magnetic moments are 2 μB We use the same method to modulate ZnS:Co with N, but we do not get same results.(3) The magnetic and optical properties Co/Fe co-doped ZnS was calculated. When one Mn and one Co are connected at the same S2-, the AFM states is stable and the total magnetic moment is 2 μB. The calculation of imaginary dielectric function indicates the optical gap is 0.6 eV. There is a 0.1 eV red shift comparing with that of pure Co-doped ZnS.