Interplay of local moment and itinerant magnetism in cobalt-based Heusler ferromagnets: Co₂TiSi, Co₂MnSi and Co₂FeSi

Heusler ferromagnets based on Co are important materials for spintronics due to the exceptional combinations of high Curie temperature and strong spin polarization. We investigate the electronic structure, magnetism and spin excitations in the cobalt-based full Heusler compounds, Co2TiSi, Co2MnSi and Co2FeSi using first principles calculations. Co2TiSi and Co2MnSi are half-metals, while Co2FeSi is not. The trends in the Curie temperature of Co2MnSi and Co2FeSi are well reproduced by the calculated spin wave dispersions. Remarkably, Co2TiSi is a very itinerant magnet, while both Co2FeSi and Co2MnSi show local moment behavior regarding the Fe and Mn, while retaining the itinerancy of the Co magnetism. Although our results do not support the half-metallic character proposed for Co2FeSi, consistent with the reported high Curie temperature, we find a very strong positive transport spin polarization, which combined with the large moment, cubic structure and high Curie temperature supports the further investigation of Co2FeSi as a material for spintronic applications.