Pecularities of Hall effect in GaAs/δ〈Mn〉/GaAs/InxGa1−xAs/ GaAs (x ≈ 0.2) heterostructures with high Mn content

The transport properties of GaAs/δ〈Mn〉/GaAs/In x Ga1−x As/GaAs structures containing an In x Ga1−x As (x ≈ 0.2) quantum well (QW) and a Mn delta layer (DL) with relatively high content, about one Mn monolayer (ML), are studied. In these structures the DL is separated from the QW by GaAs spacer with thickness d s = 2–5 nm. All structures possess a non-metallic character of conductivity and display a maximum in the resistance temperature dependence R xx (T) at the temperature ≈ 46 K, which is usually associated with the Curie temperature T C of ferromagnetic (FM) transition in DL. However, it is found that the Hall effect concentration of holes p H in the QW does not decrease below T C as one ordinary expects in similar systems. On the contrary, the dependence p H (T) experiences a minimum at T = 80–100 K depending on the spacer thickness, then increases at low temperatures more strongly when d s is smaller, and reaches a giant value p H = (1–2) × 1013 cm−2. The obtained results are interpreted in the terms of magnetic proximity effect of the DL on the QW, inducing spin polarization of the holes in the QW. Strong structural and magnetic disorder in the DL and in the QW, leading to phase segregation in them is taken into consideration. The high p H value is explained as a result of the compensation of the positive normal Hall effect component by the negative anomalous Hall effect component.