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A complex approach to the short-range ordering in molten binary cadmium and zinc antimonides has been proposed which considers specific features of the fine structure of chemical bond and interatomic interaction in АIIВV semiconductors. A procedure has been developed and the dissociation energies of nonequivalent chemical bonds in cadmium and zinc antimonides have been calculated as a function of interatomic distances and atomic characteristics of the starting components.

We have studied the caloric and magnetic properties of alloys in the MnAs–ZnGeAs2 eutectic system. The results demonstrate that the heat effect and temperature range of the ferromagnetic-to-paramagnetic phase transformation depend on the crystallite size of manganese arsenide. Reducing the crystallite size to ≤60 nm causes the heat effect of the transformation to disappear, significantly changes the temperature range of the magnetic transition, and raises the Curie temperature of the alloy to 351 K.

We determined, using a set of physicochemical methods, including X-ray powder diffraction (XRD), differential thermal analysis, and microstructure studies, that the CdAs2–Cd3As2–MnAs ternary system is bounded by three eutectic-type quasi-binary sections: Cd3As2–MnAs, CdAs2–MnAs, and Cd3As2–CdAs2. For Cd3As2–MnAs and CdAs2–MnAs sections, the eutectic coordinates are, respectively, 75 mol % Cd3As2 + 25 mol % MnAs, T m.eut = 604°C; and 92 mol % CdAs2 + 8 mol % MnAs, T m.eut = 608°C. These are rod eutectics. Manganese solubilities in Cd3As2 and CdAs2 phases are insignificant and, according to XRD and SEM, they do not exceed 1 at %. The binary eutectics of the quasi-binary sections form ternary eutectic Cd3As2 + CdAs2 + MnAs, whose average composition as probed by SEM is 34.5 at % Cd, 63 at % Cd and 2.5 at % As and T m.eut = 600°C. Cadmium and manganese arsenide alloys are ferromagnets with the Curie point at ~320 K. The magnetic and electric properties are due to ferromagnetic MnAs microinclusions.

Phase diagram in the ZnSiAs 2 –MnAs nanocomposite system was studied by Х-ray, DTA and SEM. The system has an eutectic character. The coordinates of eutectic are 87±1 mol% MnAs and 847±10 °C. The eutectic consists of the manganese arsenide lattice with ZnSiAs 2 inclusions.

The ZnAs2–MnAs system, characterized by X-ray powder diffraction, differential thermal and microstructure studies, is of the eutectic type, with the coordinates of eutectic 73 mol% ZnAs2 and 27 mol% MnAs and Tm = 716 °C. The solubility of MnAs in ZnAs2 is lower 1 mol%. Alloys of ZnAs2 with MnAs are ferromagnetic with Tc ≈ 318 K, their magnetization being increased with raising the MnAs content.

We present the results of structural characterization of Cd1 � xMnxGeAs2 chalcopyrite-type crystals with low Mn content x varying from 0 to 0.037. High resolution X-ray powder diffraction method of measurements and Rietveld refinements procedure used for analysis of obtained diffraction patterns revealed high crystal quality of the samples. The substitutional alloying of Cd1 � xMnxGeAs2, with Mn ions at Cd sites, has been confirmed. The analytical equations describing the linear reduction of the lattice parameters with increase of Mn content were deduced and compared with the literature results of theoretically estimated lattice parameters of compounds of the same kind. Copyright © 2015 John Wiley & Sons, Ltd.

Six equilibrium samples of (1 − x )ZnSnAs 2 + x MnAs ( x = 0, 0.1, … 0.5 mol.%) and one quenched sample of 0.8ZnSnAs 2 + 0.2MnAs were synthesized. The samples were studied with X-ray, DTA, MFM and SEM. The system ZnSnAs 2 –MnAs has eutectic point with coordinates 45 ± 2 mol.% MnAs and 744 ± 10 °C. The eutectic compound contains isolated, practically round shape inclusions of MnAs in the host ZnSnAs 2 . Based on the earlier investigations, we predict negative magnetoresistance effect in this semiconductor–ferromagnet compound with nanogranular structures. The lattice parameters of ZnSnAs 2 without manganese arsenide and ZnSnAs 2 + MnAs are similar, meaning MnAs does not influence the lattice parameters. Therefore one can make conclusion that solubility of the MnAs in ZnSnAs 2 is low. The lattice parameters are a = 5.8509 A, c = 11.7135 A for tetragonal and a = 5.8558 A for cubic symmetry. The density of the ZnSnAs 2 calculated from the HR-XRD is 5.5314 g/cm 3 for tetragonal and 5.5230 g/cm 3 for cubic structure.

The phase equilibria in the ZnGeAs 2 –CdGeAs 2 system were investigated by X-ray, DTA, EDXRF, microstructure observations and SEM. The solid solutions are present in all range of concentrations above 440 °С. Below this temperature a decay region of solid solution of Zn 1− x Cd x GeAs 2 is observed in the range of concentrations x = 0.19–0.92 at room temperature. The investigation of the system was obstructed by liquation and segregation processes occurring during the synthesis.

A new ferromagnetic material based on a Cd3As2 + MnAs composite with the Curie point of 320 K has been prepared. Magnetic and electrical properties of the composite have been found to be determined by manganese arsenide nanoclusters. The composite has metallic conduction. Its resistance decreases with increasing magnetic field both at low and room temperatures, indicating spin-dependent scattering mechanisms and exchange interactions between magnetic nanoclusters in the composite.

We have measured the resistivity and relative bulk compressibility of Zn1 − xMnxGeAs2 (x = 0.02 and 0.4) samples at hydrostatic pressures of up to 9 GPa. The pressure dependences of the resistivity and relative compressibility demonstrate sharp changes in resistivity and volume. The changes occur at the same high pressure, attesting to a structural phase transition.

The phase diagram of the ZnGeAs2-CdGeAs2 system was constructed using a set of physicochemical analysis methods (X-ray powder diffraction, differential thermal, and microstructural analyses). It was shown that there is a continuous series of solid solutions ZnxCd1 − xGeAs2 in the system at temperatures above 600°C. At temperatures below 600°C, there is a significant phase separation region. The solubility at room temperature on the side of ZnGeAs2 does not exceed 12 mol % CdGeAs2, and that on the side of CdGeAs2 is no more than 16 mol % ZnGeAs2. The change in the crystal lattice parameters of the solid solutions within these concentration ranges obeys Vegard’s law, which is indicative of the mutual replacement of Zn and Cd in the cation sublattice of the compounds ZnGeAs2 and CdGeAs2.

We have synthesized a new ferromagnetic material based on a Zn3P2 + MnP composite with a Curie temperature of 290 K. Experimental data demonstrate that its magnetic and electrical properties are determined by manganese phosphide nanoclusters. The composite has metallic conductivity. Its electrical resistance drops with increasing magnetic field, and its magnetoresistance in a magnetic field of 14 T at 7 K reaches 9%.

We have been studying magnetic properties of magnetic ion clusters in ternary, quaternary, and quinary IV-VI and II-IV-V 2 diluted magnetic semiconductors with varying concentrations of different magnetic and non-magnetic cations. We observed clusters of different types, from non-random distribution of magnetic ions in the host lattice to precipitates with the crystalline structure different from that of the host. The size of such precipitates varied from 200 nm to 20 μm. Depending on the type and size of clusters we observed different magnetic properties of the compounds, such as paramagnetic, spin-glass, spin-glass-like, or ferromagnetic states. For example, Zn 1-x Mn x GeAs 2 compounds with x ≤ 0.053 were paramagnetic with evidence of small short-range magnetic interactions, while in the same material with x ≥ 0.078 we observed room-temperature ferromagnetism. In IV-VI DMS clusters usually created a spin-glass or spinglass- like state. However, in some Ge 1-x-y Pb x Mn y Te crystals we observed a co-existence of two very different spin-glasslike states with transition temperatures T 1 ≈ 5 K and T 2 ≈ 90 K.

The resistivity (ρ) and Hall coefficient (RH) of n-Cd1 − xCoxGeAs2 with x = 0.05–0.15 were measured as functions of temperature (at atmospheric pressure) and pressure (up to p = 7 GPa). The temperature-dependent ρ data were used to determine the ionization energy of a cobalt-related impurity center. In the ρ(p) and RH(p) curves, we identified structural semiconductor-semiconductor phase transitions under both increasing and decreasing pressure. Using a mixed-phase structure-effective medium model, we assessed the dynamics of the variation of phase composition with pressure.

Cd0.81Mn0.19GeP2 dilute magnetic semiconductor (DMS) has been subjected to a complex study of electric and magnetic properties under high hydrostatic pressures of up to 7 GPa with pressure rise and release. Electrical resistivity, Hall factor, transverse magnetoresistance, relative magnetic susceptibility, and volume magnetostriction have been measured. Compressibility (k) and spontaneous magnetization coefficient (ωS) have been calculated.

We have studied the effect of high pressures on the electrical and magnetic properties of dilute magnetic semiconductor Cd0.82Mn0.18GeAs2. Electrical resistivity, Hall coefficient, transverse and longitudinal magnetic resistance, and magnetic susceptibility have been measured under high pressures (up to 9 GPa). The energy of a manganese impurity level was estimated at 155 meV from electrical resistivity and Hall factor versus temperature curves at the atmospheric pressure. Structural and magnetic phase transitions have been discovered in Hall resistance versus magnetic field curves measured at various temperatures; abnormal and normal Hall factors have been calculated.

The systematic studies of both magnetic and magnetotransport properties of Zn 0.947 Mn 0.053 GeAs 2 diluted magnetic semiconductor are presented. The paramagnetic behaviour of the sample confirms that the solubility of Mn in the studied alloy is of the order of 5 at%. The Curie―Weiss behaviour of magnetic susceptibility is preserved only at low temperatures, T < 100 K indicating the presence of short-range magnetic interactions in the system due to the presence of groups of Mn counting few ions. The high-field magnetization together with magnetoresistance data is used to estimate the amount of magnetic ions active in the semiconductor matrix. The obtained results showed that the amount of magnetically active Mn ions in the semiconductors matrix is two orders of magnitude lower than the value obtained from X-ray fluorescence measurements. The magnetotransport studies revealed that only about 30% of all Mn ions are electrically active in the semiconductor matrix.

The heterostructure ferromagnetic/semiconductor ZnSiAs2/Si was obtained by using the Si-ZnAs2 phase diagram. The magnetic properties of Zn1-XMnXSiAs2 bulk crystals and ferromagnetic layered heterostructures were similar. The same method was used for preparing a ferromagnetic layer ZnGeAs2 on a germanium substrate.

New diluted magnetic semiconductors (CdGeAs2:Mn, ZnGeAs2: Mn, and ZnSiAs2: Mn chalcopyrites) were synthesized. Magnetization M, electrical resistivity, magnetoresistance, and the Hall effect of these compositions were examined. Although the M(T) curves are complicated, they are similar in shape, for which the concentration and mobility of the charge bearers. Their Curie points are higher than 300 K, the highest in systems of the AIIBIVC2V: Mn type.

A new p -type dilute magnetic semiconductor was synthesized on the basis of manganese-doped ZnSiAs 2 chalcopyrite. As the manganese percentage in ZnSiAs 2 increased, the Curie temperature increased from 325 to 337 K for compositions containing 1 and 2 wt % manganese. The ferromagnetic properties of the new dilute magnetic semiconductor were due to nanoclusters that were generated by concurrent substitution of manganese for elements in the cationic sublattice of chalcopyrite.

Bulk and film samples of manganese-doped zinc-silicon diarsenide are obtained. Investigation of electrical and magnetic properties of ZnSiAs2: Mn samples showed that they possess the combination of ferromagnetic and semiconductor properties at above room temperature and are of interest as materials for spin transport.

The electrical resistivity and Hall coefficient of the high-temperature ferromagnetic semiconductor p-Zn1 − xCdxGeAs2〈Mn〉 have been measured as a function of pressure near room temperature. The features in the curves obtained attest to a structural phase transition at particular pressures. With increasing manganese content, the phase transition shifts to lower pressure. The features observed in the pressure-dependent Hall coefficient of the crystals containing more than 0.06 wt % manganese, in which ferromagnetic behavior is more pronounced, are probably due to the anomalous component of the Hall effect and its modulation in the presence of narrow impurity bands.

Mn-doped ZnSiAs2/Si heterostructures were grown by vacuum-thermal deposition of ZnAs2 and Mn layers on Si substrates followed by annealing. The surface contained a ZnSiAs2 film, but also micro-crystals with a composition close to ZnAs2 or ZnSiAs2-Si-SiAs eutectic. The temperature and field dependencies of the magnetization were measured. Two types of magnetic phases were detected: a paramagnetic one with the mean magnetic moment of 7.6 Bohr magnetons, formed by Mn2+ ions, and a ferromagnetic one with Curie temperature 340 K in 50 kOe magnetic field, formed by MnAs clusters. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Computer simulations were performed to increase the quantum efficiency of LED by optimizing the nanoheterostructure (NH). Furthermore, the InGaN and AlGaP NHs for LEDs were optimized. On the basis of the optimum NH, ways to further increase the efficiency and the influence of impurities and indium atoms doped into barriers between quantum wells were investigated. The optimum impurity and indium atom concentrations to achieve higher flux were determined.

Results of investigation of n-type Bi2-xMnxTe3with x≈0.025 grown by the Bridgman method are presented. Structural properties are studied by means of x-ray diffraction, EDX and positron lifetime spectroscopy. Results of AC magnetic susceptibility measurements and electronic magneto-transport measurements show existence of ferromagnetic phase transition at 5.3 K. Effects of the phase transition on the electronic transport properties are studied.