No abstract

The structural and transport properties of GaAs/Mn/GaAs/InxGa1−xAs/GaAs quantum wells (x≈0.2) with Mn δ-layer (4–10 at. %), separated from the well by a GaAs spacer, have been studied. The hole mobility in the investigated structures has exceeded the values known for magnetic III-V heterostructures by two orders of magnitude. For structures with the conductivity of the metal type, we have succeeded to observe at low temperatures Shubnikov–de Haas oscillations just confirming the two dimensionality (2D) of the hole energy spectrum. Exactly those 2D holes promote the ferromagnetic ordering of the Mn layer. That has been proven by (i) observing maxima (at 25–40 K) in temperature dependencies of the resistance, which positions agree with calculated values of Curie temperatures (for structures with the indirect interaction of Mn atoms via 2D holes), and (ii) revealing the negative spin-dependent magnetoresistance (NMR) as well as the anomalous Hall effect (AHE), which values are also in good agreement with calculations relating to ferromagnetic 2D III-V systems. As for the structures with the insulator type of the conductivity, their NMR and AHE features evidence the phase separation—the sample fragmentation with the formation of mesoscopic ferromagnetic areas separated by paramagnetic strata of the high tunnel conductivity.

We report results of investigations of the structural and transport properties of GaAs/Ga1−xInxAs/GaAs quantum wells (QWs) having a 0.5–1.8 monolayer (ML) thick Mn layer, separated from the QW by a 3 nm thick spacer. The structure has hole mobility of about 2000 cm2 (V s)−1, being by several orders of magnitude higher than in known ferromagnetic two-dimensional (2D) structures. The analysis of the electro-physical properties of these systems is based on detailed study of their structure by means of high-resolution x-ray diffractometry and glancing-incidence reflection, which allow us to restore the depth profiles of the structural characteristics of the QWs and thin Mn-containing layers. These investigations show the absence of Mn atoms inside the QW. The quality of the structures was also characterized by photoluminescence spectra from the QWs. The transport properties reveal features inherent to ferromagnetic systems: a specific maximum in the temperature dependence of the resistance and the anomalous Hall effect (AHE) observed in samples with both ‘metallic’ and activated types of conductivity up to ∼100 K. AHE is most pronounced in the temperature range where the resistance maximum is observed. The results are discussed in terms of the interaction of 2D-holes and magnetic Mn ions in the presence of large-scale potential fluctuations related to the random distribution of Mn atoms. The AHE values are compared with calculations taking into account the ‘intrinsic’ mechanism in ferromagnetic systems.

No abstract

Absence of anomalous Nernst effect in spin Seebeck effect of Pt/YIG AIP Advances 6, 015018 (2016); 10.1063/1.4941340Dual resonant structure for energy harvesting from random vibration sources at low frequency AIP Advances 6, 015019 (2016) The results of a comprehensive study of magnetic, magneto-transport and structural properties of nonstoichiometric Mn x Si 1-x (x≈0.51-0.52) films grown by the Pulsed Laser Deposition (PLD) technique onto Al 2 O 3 (0001) single crystal substrates at T = 340 • C are present. A highlight of used PLD method is the non-conventional ("shadow") geometry with Kr as a scattering gas during the sample growth. It is found that the films exhibit high-temperature (HT) ferromagnetism (FM) with the Curie temperature T C ∼ 370 K accompanied by positive sign anomalous Hall effect (AHE); they also reveal the polycrystalline structure with unusual distribution of grains in size and shape. It is established that HT FM order is originated from the bottom interfacial self-organizing nanocrystalline layer. The upper layer adopted columnar structure with the lateral grain size ≥ 50 nm, possesses low temperature (LT) type of FM order with T c