Band structure evolution and the origin of magnetism in (Ga,Mn)As: From paramagnetic through superparamagnetic to ferromagnetic phase

Abstract

The authors investigate the development of magnetic phases in (Ga,Mn)As -- the canonical dilute ferromagnetic semiconductor -- in a thoroughly prepared set of high-quality layers grown by molecular beam epitaxy. The Mn content in the (Ga,Mn)As solid solution extends from the extremely diluted (0.0007% Mn) to the medium Mn content of 1.6%. The authors trace simultaneously the evolution of magnetic and electronic properties of (Ga,Mn)As by comprehensive magnetic (SQUID magnetometry) optical (Raman scattering and photoreflectance) and ARPES measurements. The onset of a low-temperature ferromagnetic phase in (Ga,Mn)As is revealed for 1.6% Mn, the composition just slightly above the one displaying purely superparamagnetic behavior (0.9% Mn). No signature of a Mn-related impurity band has been identified in superparamagnetic and ferromagnetic (Ga,Mn)As.