Evidence of local moment formation in Co-based Heusler alloys

We examine the formation of local moments in Heusler alloys of the composition Co₂MnZ (where Z=Si or Al) using the combined techniques of x-ray magnetic circular and linear dichroism. The existence of local moments in half-metallic Heusler alloys is reliant upon the band gap in the minority-spin states. By utilizing the element-specific nature of x-ray absorption techniques we are able to explore the degree of localization of moments on Co and Mn atoms. We observe a crucial difference in the localization of the Co moment when comparing Co₂MnSi (CMS) and Co₂MnAl films that is consistent with the predicted larger minority-spin gap in the Co partial density of states for CMS. These results provide important evidence for the dominant role of the Co minority-spin states in realizing half-metallic ferromagnetism in this system.