Ab-initio calculations for defect energies in Co 2MnSi and Co 2CrAl

Abstract

Astract The ab-initio band calculations predict that the full-Heusler ferromagnetic alloys at L21 structure, such as Co2MnSi and Co2CrAl, are half-metallic. However, the measured spin polarizations have been usually less than ∼ 60 % . The decrease may be attributed to defects of swaps and antisites. We give ab-initio calculations for the formation energies of isolated swaps in Co2MnSi and Co2CrAl and isolated antisites in Co2MnSi, which may be the important factor to determine the defect concentrations. The present calculations predict that two kinds of antisites (Si in Mn-site and Mn in Co-site) in Co2MnSi and one kind of swap (Cr–Al) in Co2CrAl, are very likely to be formed because of the small defect energies. Using the calculated results, we clarify the fundamental features of Co2MnSi and Co2CrAl with defects and discuss how to understand the discrepancies between the band calculation and experimental results.