Ab initio predictions for the effect of disorder and quarternary alloying on the half-metallic properties of selected Co2Fe-based Heusler alloys

Co2Fe-based Heusler alloys possess high Curie temperatures and magnetization, therefore they are the most studied compositions for spintronics applications. Here we report ab initio calculations to investigate the effect of structural disorder on the theoretical spin polarization and magnetization in ternary Co2.25-xFe0.75+xSi alloys. Quarternary Heusler alloys with substitution of Mn or Cr for Fe, and gradual replacement of Si by Al or Ga in the Co2FeSi composition, were also studied. For high Fe concentration alloys, the Slater-Pauling rule is preserved if a small on-site Coulomb exchange is taken into account in the calculations. In such a case, the change in the total number of valence electrons by alloying was found to be an efficient way to tailor the half-metallic behavior with high resistance against structural disorder. The necessity of the on-site correlation in these alloys to the correct description of magnetic and electronic structure is also addressed.