Kronast, F.; Ovsyannikov, R.; Vollmer, A.; Dürr, H.A.; Eberhardt, W.; Imperia, P.; Schmitz, D.; Schott, G.M.; Rüster, C.; Gould, C.; Schmidt, G.; Brunner, K.; Sawicki, M.; Molenkamo, L.W.: Mn 3d electronic configurations in (Ga1-xMnx)As ferromagnetic semiconductors and their influence on magnetic ordering. Physical Review B 74 (2006), p. 235213/1-8
10.1103/PhysRevB.74.235213
Abstract:
We applied x-ray absorption spectroscopy and x-ray magnetic circular dichroism XMCD at the Mn 2p-3d resonances to study the Mn 3d electronic configuration and the coupling of Mn 3d magnetic moments in various Ga1−xMnxAs films. The homogeneity of the Mn depth profile throughout the Ga1−xMnxAs film was tested by additional structure-sensitive x-ray resonant reflectivity measurements. In all investigated Ga1−xMnxAs films the electronic and magnetic configuration of the Mn impurities varies throughout the Mn-doped layer. This inhomogeneity is caused by the surface segregation of nonferromagnetic Mn in a d5 configuration. X-ray resonant reflectivity data show that the accumulation of nonferromagnetic Mn near the surface is strongly enhanced by low-temperature annealing. By XMCD we identified the Mn species responsible for the long-range ferromagnetic coupling. It is characterized by an Mn 3d5-3d6 mixed-valence acceptor state that is unchanged at all investigated Mn concentrations, ranging from 1% to 6%. Additional nonferromagnetic Mn occurs in the bulk of high-concentration samples. We discuss a model in which the latter is due to antiferromagnetic Mn-Mn nearest-neighbor pairs.