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Structural and magnetic properties of the group III-V diluted magnetic semiconductor In1-xMnxSb with x = 0.005-0.06, including the nuclear magnetic resonance (NMR) investigations, are reported. Polycrystalline In1-xMnxSb samples were prepared by direct alloying of indium antimonide, manganese and antimony, followed by a fast cooling of the melt with a rate of 10-12 K/s. According to the X-ray diffraction data, part of Mn is substituted for In, forming the In1-xMnxSb matrix. Atomic force microscopy and scanning tunneling microscopy investigations provide evidence for the presence of microcrystalline MnSb inclusions (precipitates), having a size of ∼100-600 nm, and the fine structure of nanosize grains with a Gaussian distribution around the diameter of ∼24 nm. According to the NMR spectra, the majority of Mn enters the MnSb inclusions. In addition to the single Mn ions, which contribute to the magnetization M (T) only in the low-temperature limit of T < 10-20 K, and MnSb nanoprecipitates responsible for the ferromagnetic (FM) properties of In1-xMnxSb, a superparamagnetic (SP) contribution of atomic-size magnetic Mn complexes (presumably dimers) has been established. The fraction of the MnSb phase, η ∼ 1-4%, as well as the concentration, nsp ∼ (0.8-3.2) × 1019 cm-3, and the magnetic moment of the Mn dimers, μ ∼ 8-9 μB, are determined. The solubility limit of Mn in the InSb matrix, NSL ∼ 1020 cm-3, is estimated. Hysteresis in low (H < 500 Oe) magnetic fields and saturation of the magnetization in high (H > 20 kOe) magnetic fields are observed, indicating a presence of the SP and FM contributions to the dependence of M (H) up to T ∼ 500 K. The hysteresis is characterized by the coercivity field, Hc, decreasing between ∼100 and 75 Oe when T is increased from 5 to 510 K. The values of Hc are in reasonable agreement with the effect of the largest MnSb inclusions. The maximum of M (T), measured in the zero-field-cooled and the field-cooled conditions in a weak field of 500 Oe, is observed at T ∼ 510 K and is attributable to the Hopkinson effect. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The experimental data of the temperature-dependent Hall-effect measurements on Mn-doped p -type InSb samples, which exhibit the anomalous sign reversal of the Hall coefficient to negative at low temperatures, have been analyzed on the basis of the nearest-neighbor hopping model in an impurity band. It is shown that the anomalous sign reversal of the Hall coefficient to negative can be well explained with assuming the hopping Hall factor in the form of Ahop = ( kB T / J3) exp ( KNNH T3/ T) with the negative sign of J3. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic and photoluminescent properties of manganese-doped ZnSe crystals with different impurity concentrations were investigated. The concentration of Mn2+ ions in ZnSe crystals has been varied from 0.01 to 0.3at%. Magnetic and photoluminescent studies have confirmed the introduction of Mn in ZnSe crystals. It was established that Mn2+ ions are responsible for the emission bands with maximum at 616nm and 633nm, which correspond to 4T2→6A1 and 4T1→6A1 intracentre transitions of Mn2+ ions respectively. It was found that the concentration quenching of the photoluminescent bands is associated with Mn2+ ions, which are due to the formation of Mn–Mn clusters. Magnetic properties studies have shown that at high doping levels the manganese atoms form Mn–Mn clusters in ZnSe. From the temperature dependence of magnetic susceptibility of ZnSe:Mn crystals that follows the Curie–Weiss law, it was possible to estimate the Curie–Weiss temperature Θ(x) and the effective Mn–Mn antiferromagnetic exchange constant (J 1). [Copyright &y& Elsevier]