Novel ferromagnetism in digital GaAs/Mn and GaSb/Mn alloys

Ferromagnetic III-Mn-V semiconductors are under intensive investigation for spintronic applications. In the present work digital alloys of GaAs/Mn and GaSb/Mn were fabricated by a combination of molecular beam epitaxy and atomic layer epitaxy. The Mn fraction in the layers was varied at constant III–V spacer thickness, and the III–V spacer-layer thickness was varied at constant Mn fraction (0.5 monolayer). Transmission electron micrographs showed good crystal quality with no evidence of three-dimensional (3D) Mn-V precipitates. The GaAs/Mn samples have Curie temperatures in the vicinity of View the MathML source and exhibit an anomalous Hall effect (AHE) similar to that seen in GaMnAs random alloys. These samples all show thermally activated resistance at zero field, characteristic of hopping conduction with evidence of Coulomb-gap-like behavior. The GaSb/Mn samples exhibit ferromagnetism (with temperature dependent hysteresis loops) and a strong AHE up to View the MathML source. At low temperatures the remanent magnetization initially drops rapidly with increasing temperature, indicative of Curie temperatures between 10 and View the MathML source depending on the Mn concentration. However, a substantial remanent magnetization persists to high temperature, suggesting a second phase with a Curie temperature above View the MathML source. These samples all showed essentially metallic behavior and weak negative magnetoresistance at low temperatures. These results are discussed in the context of a model of quasi-2D MnSb islands (for which there is direct evidence) embedded in a matrix of GaMnSb in the Mn-containing layers.