Structural and magnetic properties of Zn0.5 Co0.5 O alloy configurations via DFT
We studied the structure and magnetic properties of ZnCoO alloy configurations via spin-polarized density functional theory (DFT). For the hexagonal wurtzite Zn0.5(Co)0.5O alloy, we used a 1x1x1 ZnO unit cell in a 4-atom bilayer configuration, with one Zn atom replaced by Co. In a similar manner, we utilized a 1x1x1 CoO rocksalt structure, with four Co atoms replaced by Zn to obtain Co0.5(Zn)0.5O. We found that the original ZnO lattice did not change appreciably upon Co alloying, with around 2% compression, and thus the structure remains robust and atoms bond stronger. This is complemented by Zn0.5(Co)0.5O stronger bulk cohesive energy per formula unit (8.29 eV) compared to bulk ZnO (7.05 eV). Additionally, minimal charge redistribution between the metal atoms and oxygen is observed. On another note, a volume expansion of 3% was observed for Co0.5(Zn)0.5O, implying the formation of weaker bonds between atoms. The calculated bulk cohesive energy per formula unit for CoO is 9.47 eV, quite larger than that of Co0.5(Zn)0.5O at 8.07 eV. Lastly, our calculations showed that the net magnetization of ZnO upon Co alloying is enhanced significantly, while the reverse is true for Zn-alloyed
CoO. The results suggest that Zn0.5(Co)0.5O is more stable in hexagonal wurtzite structure and could be a better controllable ferromagnetic material for spintronics applications.