Ferromagnetism of low-dimensional structures based on III-Mn-V semiconductors in the vicinity of the insulator-to-metal transition

Abstract

The structural and transport properties of the GaAs/Mn/GaAs/InxGa1 − xAs/GaAs quantum wells (QWs) with the Mn layer distant from the QW and the Mn content ranging from 4 to 10% that correspond to the reentrant metal-to-insulator transition observed in the bulk GaMnAs are studied. The X-ray diffractometry and reflectometry are used to reconstruct the distribution profile of the Mn layers and to demonstrate the absence of the Mn atoms in the QW volume. The mobility of holes in the objects under study is greater than the known mobilities for the GaMnAs magnetic heterostructures by more than two orders of magnitude, which makes it possible to observe the Shubnikov-de Haas oscillations, proving the 2D character of the hole energy spectrum. A significant role of the 2D holes in the ferromagnetic ordering of the Mn layer is demonstrated under such conditions. The supporting evidence results from the observation of a maximum on the curves of the resistance versus temperature (at 25–40 K), whose position is in agreement with the calculated Curie temperature for the structures with indirect exchange interaction via the 2D-hole channel and the observation of the negative spin-dependent magnetoresistance (NM) and the anomalous Hall effect (AHE) that correlates with the theoretically calculated results for the ferromagnetic 2D III-Mn-V systems. The features of the NM and AHE revealed in the structures with the dielectric conduction indicate the effects of phase separation lying in the fragmentation of the sample into mesoscopic ferromagnetic domains separated by tunnel transparent paramagnetic layers. Such NM and AHE features are also observed in the weakly dielectric InMnAs films, which points to an important role of such effects in the III-Mn-V systems in the vicinity of the insulator-to-metal transition.