Effects of defects on the half metallicity of a Mn/Si digital ferromagnetic heterostructure

The effects of defects on the half-metallic properties of the Mn/Si digital ferromagnetic heterostructure (DFH) (PRL \textbf{96}, 027211 (2006)) are investigated using a first principles density-functional theory approach. The half metallicity is retained when the $\delta $-layer of the Mn atoms has a vacancy or a Si imperfection. However, the the half metallicity is destroyed if the $\delta $-layer spreads because of the increased d-d bonding of the defect makes the d-p hybridization imperfect.