Revisiting half-metallicity of Co-based full Heusler alloys from non-empirical DFT+U method

The half-metallic (HM) ferromagnet, which has 100% spin polarization at the Fermi level (E_F), is great advantage to enhance efficiency of spin-dependent tunneling property. In particular, Co-based full Heusler alloys have been paid much attention because of the HM and high Curie temperature. The density functional theory (DFT) calculations are expected to play a key role for searching the HM materials and understanding an origin of HM. However, the DFT methods within the local density approximation often fail to predict the HM due to localized d electrons around E_F. In this work, we revisit electronic structure of Co₂MnSi by the DFT+U method, where +U parameters representing correlation effect are derived from linear response theory. We revealed important atomic orbital hybridizations, which mainly dominate energy gap at E_F. Although the Co₂MnSi is not HM, our energy diagram provides a new guideline to tune the HM gap. We extended our calculations to quaternary systems Co₂(Y,Mn)Si, where Y is 3d transition metals. We found the systems with Y of Ti, V, Cr, and Fe show the HM when composition of Y is selected appropriately.