Fachgruppe Nanostrukturierte Materialien    

In this review, we describe the structural, magnetic and magnetotransport properties of one of the most advanced ferromagnetic semiconductor material systems, (Ga,Mn)As/GaAs heterostructures and nanostructures. Molecular beam epitaxy at low substrate temperature is applied to deposit epitaxial layers without MnAs cluster formation but with homogeneous incorporation of substitutional Mn up to about 8% content and with concomitant hole carrier densities in the 1021 cm–3 range. Epitaxial strain, Mn content, p-doping and defects that are related to low-temperature growth may strongly influence the ferromagnetic properties, like Curie temperature, remanent magnetization and magnetic anisotropy. This is well understood within the Zener model for ferromagnetic ordering of Mn ions that is mediated by p–d exchange interaction with free holes in the complex, anisotropic valence band states. The interplay of ferromagnetism and electronic band structure manifests in the various magnetotransport phenomena, like anomalous Hall effect and spin valve tunneling transport. In particular, tunneling structures reveal many novel features, such as the tunneling anisotropic magnetoresistance (TAMR), that highlight the interplay of magnetic and electronic properties and may be pathways to future spintronics devices.