A first-principles study on magnetic properties of the intrinsic defects in wurtzite ZnO

Since the origin of magnetism in ZnO-based diluted magnetic semiconductors (DMSs) is still controversial, in this work, we presented a detailed study on the magnetic, structural, and electronic properties of wurtzite ZnO-based DMS systems with point and complex intrinsic defects. Two outer electrons from neutral oxygen vacancy (V_O) occupy the a₁ orbital, making the inducted magnetic moment to be zero, while a cluster including three V_Os leads to a magnetic moment of ∼1 μ_B. The magnetic moment of the system with a Zn vacancy (V_Zn) is 1.65 μ_B. When two neutral V_Zns in different relative distances were created in respective supercells, the systems showed different magnetic moments induced by the unequal level between the highest electron occupied orbital of the defect state introduced by different V_Zn sites and the valence band maximum. The system of a neutral O occupying an octahedral site gives rise to a magnetic moment of 2 μ_B, while zinc interstitial and antisite defects do not cause spin polarization. The system with a complex defect of V_O and V_Zn is magnetic when those vacancies are adjacent but still do not cause the compensation effect. The oxygen interstitial defect is unstable, and V_Zn easily turns into the complex defect. We suggest that V_O clusters and V_Zn complex defects could likely be the origin of ferromagnetism in undoped ZnO.