First-principles Calculation Of Magnetic Properties In Zno-based Diluted Magnetic Semiconductors

The electronic structures of ZnO and Mn, V doped ZnO-based diluted magnetic semiconductors with and without defects were calculated by the first-principles calculation based on density functional theory. The influences of intrinsic defects on the band structure of ZnO were investigated and the magnetic interactions in the ZnMnO and ZnVO systems were analyzed.The analysis of density of states and band structures shows that pure ZnO is a direct band gap semiconductor and its band gap is formed through the bonding and anti-bonding interactions between O2p and Zn4s so thant Zn4s states and O2p states are repulsed upward and downward, respectively. The calculations of the electronic structures of ZnO with 0 vacancy and Zn vacancy indicate that the two types of defects all make the band gap of ZnO increased, and donor levels nearby the conduction band were introduced by 0 vacancy while acceptor levels nearby the valence band were introduced by Zn vacancy.The calculations of electronic structures of V doped ZnO with and without defects suggest that the ferromagnetism of ZnVO systems originated from the pd hybridization of V3d states and O2p states, the magnetic monments decreased with the introduction of Zn vacancy because of the decrease of 3d electron population and the decrease of the ratio of d states and p states in pd hybridization. The magnetic monments increase with the introduction of 0 vacancy because the energy level of O vacancy is close to that of V impurity, then the electrons in 0 vacancy hop to the partially occupied 3d-orbitals of V ions and the neighboring V ions have parallel magnetic moments. Besides, the electrocnic spin densities show that Zn vacancy makes the spins of the electrons be favor to parallel to minority while 0 vacancy makes the spins of the electrons be favor to parallel to majority, which result in the weak ferromagnetism with Zn vacancy in doped system and strong ferromagnetism with 0 vacancy in doped system.The calculation of the electronic structures of Mn doped ZnO shows that ZnMnO systems might produce ferromagnetism, antiferromagnetism and paramagnetism as the changes of the substitution sites of Mn atoms in ZnO lattice. When the ZnMnO systems exist antiferromagnetism, the introduction of 0 vacancy could make the antiferromagnetism of ZnMnO systems more stable than that with no defects, and the existence of Zn vacancy could change the Mn doped ZnO system to ferromagnetism because of the hybridization between Mn3d states and the impurity states of Zn vacancy whose energy are closed to each other and the enhancement of the hybridization between Mn3d states and O2p states.