First-principles Study of the Electronic, Magnetic and Structural Properties of ZnO and Zn 1-x Cr x O (x = 0.125, 0.25, 0.375, 0.5) in the Room Temperature Wurtzite Structure

First-principles electronic structure calculations were presented to study the electronic, magnetic and structural properties of pure ZnO and Zn_1-xCr_xO (x = 0.125, 0.25, 0.375, 0.5) in the room temperature (293 K) wurtzite structure. Pure ZnO is found to be a non-magnetic insulator due to perfectly paired electrons in each Zn-3d orbital. This material encounters nonmagnetic insulator to a ferromagnetic half-metal for x 0.125 and then to a ferro^magnetic ^metal for x = 0.25. The ferromagnetic metallic phase maintains up to x = 0.5. It is revealed in this study that 100% spin polarization is responsible for the half-metallic behaviour of Zn_0.875Cr_0.125O. Nevertheless, partial filling of Cr-3d_3z²-r² orbital in the spin-up channel together with a minute, but finite contribution of electrons from the Cr-3d_{xy/z²- r²} orbitals at EF for the spin-down channel are together responsible for the metallic behaviour of Zn_1-xCr_xO (x ≥ 0.25). The ferromagnetism in all the Cr-substituted compounds arises from strong Hund’s rule coupling. Eventually, a trivial variation in the Zn-O/Zn-Zn bond distances and ZZn-O-Zn bond angles caused by Cr doping is responsible for a minor structural distortion in Zn_0.5Cr_0.5O.