Interfacial structure and half-metallic ferromagnetism in Co2 MnSi -based magnetic tunnel junctions

X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) techniques are utilized to explore the ferromagnetic/barrier interface in Co2 MnSi full Heusler alloy magnetic tunnel junctions. Structural and magnetic properties of the interface region are studied as a function of the degree of site disorder in the alloy and for different degrees of barrier oxidation. Photoelectron scattering features that depend upon the degree of L 21 ordering are observed in the XAS spectra. Additionally, the moments per 3d hole for Co and Mn atoms are found to be a sensitive function of both the degree of L 21 ordering and the barrier oxidation state. Significantly, a multiplet structure is observed in the XMCD spectra that indicates a degree of localization of the moments and may result from the half-metallic ferromagnetism (HMF) in the alloy. The magnitude of this multiplet structure appears to vary with preparation conditions and could be utilized to ascertain the role of the constituent atoms in producing the HMF, and to examine methods for preserving the half-metallic state after barrier preparation. The changes in the magnetic structure caused by barrier oxidation could be reversed by inserting a thin Mg interface layer in order to suppress the oxidation of Mn in the Co2 MnSi layer.