Since the discovery of ferromagnetism in (Ga,Mn)As the long-range coupling between Mn spins has been ascribed to spin-polarization of valance band holes. Recent experiments indicate, however, that the spin alignment is rather mediated by an impurity band. Since ferromagnetism is observed at rather low Mn concentrations (around 1.5%), the question is if the interaction between Mn-induced states is sufficient to provide delocalized states. We have used resonant photoemission around the Mn2p threshold to study the Mn-induced valence band structures in as-grown (Ga,Mn)As samples with Mn concentrations ranging from 0.1% to 5%. Our data show that there is indeed a clear broadening already around 1% Mn. Our data thus provide direct support for the impurity band model.
Magnetic semiconductor, photoemission
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