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B.A. Aronzon (1,2), A.S. Lagutin (1), V.V. Rylkov (1,2), A. Lashkul (3), R. Laiho (4)
1 Russian Research Center "Kurchatov Institute", Moscow, 123182 Russia 2 P.N. Lebedev Research Center in Physics, Leninskii Ave. 53, Moscow, 119991 Russia 3 Lappeenranta University of Technology, P.O.Box 20, FIN-53851 Lappeenranta, Finland 4 Vihuri Physical Laboratory, Department of Physics, University of Tyrku, FIN-20014, Finland A search of materials with the controllable spin polarization of charge carriers is among the most topical issues of spintronics. In this connection, Dilute Magnetic Semiconductors (DMS) and especially A3B5-type semiconductors attract currently a widespread attention. In such materials, the spatial separation of magnetic dopants and charge carriers turned out to be promising. Having this in mind, we manufactured GaAs/InGaAs/GaAs quantum wells with a Mn ä-layer introduced into one of the GaAs layers and observed a magnetic ordering and different manifestations of the spin polarization of charge carriers. Here, we present the experimental data on the magnetization, anomalous Hall effect, magnetoresistance, and spectral density of the voltage noise, as well as the results of X-ray structural studies. The X-ray diffraction data demonstrated the absence of Mn in the quantum well. This favors the relatively high mobility of carriers (2000 cm2/Vs) as compared to the DMS-based 2D structures studied earlier and implies that the exchange interaction between the magnetic moments of Mn is nonlocal and is mediated by the charge carriers located outside the Mn layer. Due to the high mobility value the spectrum of holes is really 2D resulting in observation of the Shubnikov-de Haas oscillations and the quantum Hall effect accompany with ferromagnetic behavior, in particularly, the anomalous Hall effect at relatively high temperatures (60 K). As far as we know this is the highest Curie temperature value observed in really 2D systems based on dilute magnetic semiconductor which demonstrate quantum Hall effect and other 2D properties. At higher temperature magnetization curves are typical for magnetic cluster glass while at low temperatures the hysteretic behavior typical for ferromagnetic system was observed. Based on the obtained data, it is natural to assume that the percolation transition to the ferromagnetic state occurs at temperatures below 60 K. In such a state, the ferromagnetic percolation cluster occupies a certain p ortion of the sample volume. This transition leads to changes in the scattering rate of charge carriers and gives rise to the telegraphic noise. The magnetic ordering in the structure under study is also responsible for the peculiarities in its transport properties, giving rise to the anomalous Hall effect and the hump in the temperature dependence of the electrical resistance R(T), which is typical for systems with the ferromagnetic ordering. The temperature corresponding to the maximum in the R(T) curve agrees well with the Curie temperature calculated assuming that ferromagnetic ordering is mediated by carriers inside the quantum well. The magnitude of the anomalous Hall effect is in a good agreement with its theoretical estimations for the 2D structures based on the assumption that the dominant mechanism underlying this effect has an intrinsic origin. |
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