Theoretical investigations of Co₂Mn_1-xCr_xSn and Co₂MnSn_1-ySi_y pseudo-ternary alloys: First principles calculations

The electronic and magnetic properties of Co₂Mn_1−xCr_xSn and Co₂MnSn_1−ySi_y alloys are investigated using density functional theory (DFT) within a full-potential linearized augmented-plane-wave (FP-LAPW) method. Amongst the systems under investigation, Co₂MnSn_1−ySi_y alloys show half metallicity with 100% spin polarization at the Fermi level, however Co₂Mn_1−xCr_xSn are found to be pseudo-half metals with few minority states at the Fermi level and high spin polarization. The substitution of Si with Sn keeps the magnetic moment constant in Co₂MnSn_1−ySi_y alloys, whereas the substitution of Mn with Cr decreases the magnetic moment and degrade the half-metallicity in Co₂Mn_1−xCr_xSn alloys. The Curie temperature is calculated and it is found to be about 928 K for all Co₂MnSn_1−ySi_y alloys, whereas it decreases linearly with x for Co₂Mn_1−xCr_xSn alloys. The lattices constants, bulk modulii, energy gaps, polarization ratio and density of states are calculated and their variation versus x or y are discussed. - Highlights: • The band structure calculations show that Co₂MnSn_1−ySi_y alloys are half-metallic ferromagnets. • The effect of substituting Sn by Si is a slight change in the position of the Fermi level and an increase in the band gap. • For Co₂Mn_1−xCr_xSn alloys, the results suggest that there is a finite density of states in the minority-spin d band of manganese. • The Co₂Mn_1−xCr_xSn compounds cannot be classified as half-metallic ferromagnets. • The substitution of Mn with Cr decreases the magnetic moment per formula unit from 5.0 to 4.0µ_B