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Mn-doped GaAs is an attractive diluted magnetic semiconductor for a new spin-based electronics. It has been shown that the Curie temperature (Tc) in Ga1-xMnxAs can be raised by increasing the hole concentration as well as Mn concentration [1]. In the present study we investigated the influence of Mn delta-doping on magnetic and galvanomagnetic properties of GaAs structures with InAs quantum dot layer or GaAs/InxGa1-xAs/GaAs quantum well. All samples were prepared with the combined method of MOC-hydride epitaxy and laser deposition. Samples were grown on GaAs (100) substrate and contain InAs quantum dot layer, carbon delta-layer (to provide enhanced p-type conductivity in the quantum dot layer or in a quantum well) and laser-deposited Mn layer (with different Mn content) separated by GaAs spacers with width d=10 nm. For measurements of the magnetization in the temperature interval 4.2-400K in magnetic fields up to 7T, a SQUID magnetometer was used. The ferromagnetic phase up to 400 K was detected by SQUID magnetometer. Different magnetic phases have been found in the samples, one with Tc about 70 K, others with Tc above room temperature. The first value of Tc is very typical for hole mediated ferromagnetism in Ga1-xMnxAs solid solutions. Next phase is due to formation of MnAs clusters. Tc for bulk MnAs is about 315 K. Above this temperature ferromagnetism survived die to Ga1-xMnx clusters. Tc for such clusters depends on Mn content and may be as high as 600 K for x=0.6. In the temperature interval 4.2 - 35 K negative magnetoresistance is observed, transferring to the positive magnetoresistance. All samples had p-type conductivity and high mobility of holes. When temperature decreased sheet resistivity R samples increased. In the temperature range between 50 and 110K a kink is visible in R(T). At T
[1] T. Jungwirth, J. Sinova, J. Masek, et al, Rev. Mod. Phys., 78, 809 (2006).
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