Search

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.

The quantum anomalous Hall effect1,2 is a fundamental transport response of a topological insulator in zero magnetic field. Its physical origin is a result of an intrinsically inverted electronic band structure and ferromagnetism3, and its most important manifestation is the dissipationless flow of chiral charge currents at the edges of the system4, a property that has the potential to transform future quantum electronics5,6. Here, we report a Berry-curvature-driven4,7 anomalous Hall regime at temperatures of several Kelvin in the magnetic topological bulk crystals in which Mn ions self-organize into a period-ordered MnBi2Te4/Bi2Te3 superlattice. Robust ferromagnetism of the MnBi2Te4 monolayers opens a surface gap8–10, and when the Fermi level is tuned to be within this gap, the anomalous Hall conductance reaches an e2/h quantization plateau, which is a clear indication of chiral transport through the edge states. The quantization in this regime is not obstructed by the bulk conduction channels and therefore should be present in a broad family of topological magnets. A three-dimensional topological magnetic superlattice structure exhibits the quantum anomalous Hall effect when the Fermi energy is tuned into the correct energy window.

Semiconductor–ferromagnet alloys in the CdAs2–MnAs system were synthesized in evacuated ampules. Differential thermal analysis (DTA), X-ray powder diffraction analysis, differential scanning calorimetry, and scanning electron microscopy showed that this system is eutectic (of the acicular type), and the coordinates of the eutectic are (6 ± 0.5 mol % MnAs, Tmelt = 614 ± 1°C). The liquidus lines constructed based on the thermal events of melting in DTA are 40–50°C higher than the lines constructed based on the thermal events of crystallization, which is due to the tendency of CdAs2 toward glass transition. The synthesized alloys are ferromagnetic with TC = 315 K, and the magnetization of them increases with increasing MnAs content. The alloys with nanoinclusions ≤40 nm of the ferromagnetic phase MnAs were produced by crystallization from melts at high cooling rates (≤100 deg/s). They have a higher Curie temperature of TC = 353 K and a negative magnetoresistance of ΔR = 2% at 300 K in a saturation magnetic field of 4500 Oe, which is of practical interest for creating magnetic granular spintronic structures.

This paper presents an analytical review that addresses physicochemical principles underlying the synthesis of granular structures in semiconductor–ferromagnet systems. Such systems comprise a II–IV–V2, II2–V3, or II–V2 compound as a semiconductor and MnAs as a ferromagnet. We demonstrate that granular magnetic structures are an alternative to superlattices in spintronic devices and can exhibit giant magnetoresistance and tunneling magnetoresistance effects. It is shown that, owing to the high carrier mobility in semiconductors, they are more attractive as matrices of granular materials than are metals or dielectrics. We have formulated the basic principles underlying the synthesis of granular structures with high magnetoresistance based on eutectic systems. Eutectic crystallization involves simultaneous crystallization of all the constituent phases, leading to the formation of an unusual, fine structure. High cooling rates are favorable for metastable crystallization. This causes a synergistic effect, stimulating nanostructuring and favoring the formation of granular structures. We present results on semiconductor–ferromagnet systems and demonstrate the possibility of producing granular magnetic structures with high magnetoresistance in such systems.

We have studied the effect of hydrostatic pressure on the galvanomagnetic properties of a Cd3As2 + 20 mol % MnAs alloy in a transverse magnetic field of up to 4 kOe. The pressure dependences of the Hall coefficient and resistivity for the alloy provide evidence of reversible phase transitions. The observed negative magnetoresistance of the alloy is shown to be induced by high pressure.

Topological insulators (TI) belong to category of phases which go beyond the theory of spontaneous symmetry breaking, well describing classical phases. TI are materials of strong spin-orbit interaction that leads to the inversed band structure. Thus, they belong to different topological class than surrounding “normal” world. Consequently, these materials behave as insulators in their volume while their surface hosts metallic states, that appear as a result of the need to meet boundary conditions. The metallic states have the unusual spin structure described by the Dirac-type Hamiltonian, with the electron spin locked to its momentum. They are protected by the time reversal symmetry, thus are resistant to non-magnetic disturbances. Introducing magnetic impurities breaks the time reversal symmetry, opening the energy gap at the Dirac point and eventually modifying spin texture. In research of magnetically doped TI there are still many challenges and open questions. Here, I will present results of our recent studies of three-dimensional TI from the Bi2-xSbxTe3-ySey family, doped with Mn ions. I will discuss possible locations of Mn impurity in the crystal host lattice, the influence of doping on the crystal structure and magnetic properties. Ferromagnetism was successfully obtained in Bi2Te3 and BiSbTe3 doped with 1.5-2 at. % of Mn, with the Curie temperature of the order of ~ 15 K. The role of free carriers in ferromagnetic interactions is not clear. Ferromagnetism is observed at diluted Mn concentrations suggesting a need for a medium mediating the long-range ferromagnetic order, but the Tc does not scale with the concentration of free carriers. We would like to acknowledge National Science Center, Poland, grant no 2016/21/B/ST3/02565.

MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ it is found that migration of Mn between MnBi$_{2}$T$e_{4}$ septuple layers (SLs) and otherwise non-magnetic Bi$_{2}$Te$_{3}$ quintuple layers (QLs) has systemic consequences - it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n $\gtrsim$ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies show that Mn disorder within an SL causes delocalization of electron wavefunctions and a change of the surface bandstructure as compared to the ideal MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$. These findings highlight the critical importance of inter- and intra-SL disorder towards achieving new QAH platforms as well as exploring novel axion physics in intrinsic topological magnets., Comment: 16 pages, 5 figures, corrected typos, corrected references to figures for section 5

The magnetic susceptibility χ(T) of Zn0.1Cd0.9GeAs2 + n wt % MnAs (n = 10 or 15) ferromagnetic nanocomposites with a Curie temperature TC = 310 K has been measured as a function of temperature in the temperature range 270–350 K, and their resistivity ρ(p), Hall coefficient RH(p), and magnetization M(p) have been measured as functions of pressure near room temperature. The materials have been shown to undergo a pressure-induced ferromagnetic-to-paramagnetic phase transition, accompanied by a semiconductor–metal phase transition, at a hydrostatic pressure p ≈ 3.2 GPa and room temperature.

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.

Manganese monoarsenide samples have been prepared by the sealed-ampule technique and characterized by X-ray diffraction, differential thermal analysis, and scanning electron microscopy. The hexagonal- to-orthorhombic phase transition of MnAs has been studied using differential scanning calorimetry (DSC) and magnetic measurements. The enthalpy and temperature range of the transition have been determined to be ΔH =–5.6 J/g and 312.5–319 K, respectively. The enthalpy and temperature range of the transition are influenced by the quality of the samples. The samples containing inclusions of the metastable, orthorhombic phase have a lower enthalpy and broader temperature range of the magnetostructural transformation of manganese monoarsenide. It has been demonstrated that DSC is an effective tool for assessing the quality of MnAs samples. Temperature dependences of specific magnetization and magnetic permeability for MnAs lend support to the DSC results. From these data, the Curie temperature of MnAs has been determined to be 40°C, in good agreement with previously reported data.

The effect of high pressure on electron transport and on the field dependence of the transverse magnetoresistance has been studied in a hybrid nanocomposite based on the Zn0.1Cd0.9GeAs2 matrix and MnAs clusters. A record high negative magnetoresistance of ~74% is formed near a pressure-induced structural transition (P≈ 3.5 GPa). The considered scattering mechanisms include both the contribution from MnAs clusters at relatively low pressures (up to 0.7 GPa) and spin-dependent scattering by localized magnetic moments in the Mn-substituted structure of the matrix in the region of the structural transition. The presence of the positive magnetoresistance region associated with the two-band transport model in the high-pressure phase, as well as the large negative magnetoresistance, is described in the framework of the semiempirical Khosla–Fischer expression.

The formation of metastable Cd3Ge2As4 was established using a set of physicochemical analysis methods. The annealing of this compound at temperatures ≥450°C was shown to lead to the formation of the stable binary eutectic Cd3As2–СdGeAs2 and ternary eutectic Cd3As2–СdGeAs2–CdAs2 with the following composition (at %): Cd, 42.20; Ge, 15.69; As, 42.11; and Cd, 42.70; Ge, 15.06; As, 42.24, respectively.

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 temperature (T = 77–420 K) dependences of the electrical resistivity and the magnetization, the magnetic-field (H ≤ 5 kOe) and pressure (P ≤ 7 GPa) dependences of the resistivity, the Hall coefficient, and the magnetization have been measured in the Zn0.1Cd0.9GeAs2 + 10 wt % MnAs composite with the Curie temperature T C = 310 K. The magnetoresistive effect has been observed at high hydrostatic pressure to 7 GPa. At nearly room temperature, the pressure dependence of the magnetization demonstrated a transition from the ferromagnetic to paramagnetic state at P ~ 3.2 GPa that was accompanied by the semiconductor–metal phase transition.

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.

Electrical resistivity ρ, Hall factor R H, magnetic resistance (R m–R 0)/R 0, and magnetic-field-dependent resistances were measured in 70 mol % Cd3As2 + 30 mol % MnAs composite at fixed values of high hydrostatic pressures (up to p ≤ 9 GPa). The ρ, R H, and (R m–R 0)/R 0 versus pressure curves feature a phase transition at p = 4–4.3 GPa. Field-dependent magnetic resistance features a negative pressure-induced trend.

CdGeAs 2 is a promising material for optical applications. It has the wide transparency range between 2.3 and 18 μm except harmful absorption region at 5.5 μm. Its presence is related to the crystal lattice quality. The measurements of Raman and far infrared reflectivity spectra of the series of Cd 1− x Mn x GeAs 2 samples (0 ≤ x ≤ 0.037) were carried out in spectral range from 60 to 400 cm −1 , at room temperature. Beside all expected optical modes three defect modes are registered at about 125, 170 and 235 cm −1 . Their intensities are related to tetragonal distortion of lattice (Δ) so we connected them with lattice defects Ge As , usually formed in this material, and CdAs 2 and Cd 3 As 2 clusters whose characteristic frequencies match these values. Antisite defects Ge As are connected to energy level at about 200 meV and to absorption at 5.5 μm. Based on obtained results we can conclude that doping with small amount of manganese ( x = 0.004) results in slight deformation of CdGeAs 2 crystal lattice and consequently considerably reducing the formation of antisite defects Ge As .

The transport properties of granular Cd3As2 + MnAs (44.7% MnAs) composite structures have been studied near room temperature at high hydrostatic pressures of up to 9 GPa. The results demonstrate that the composite undergoes a structural phase transition and has a pressure-induced negative magnetoresistance.

Eutectic composites in the InSb–MnSb system have been grown by the Bridgman method in vertical geometry using a growth charge of eutectic composition. The composites consisted of a [110]-oriented single-crystal InSb matrix and single-crystal MnSb needles aligned in the growth direction. As the solidification rate was raised from 0.5 to 6 mm/h, the length of the needles increased, whereas their diameter dropped from 20 to 4 µm. Further raising the solidification rate led to spontaneous crystallization. Characteristically, the electrical and magnetic properties of the eutectic composites in the InSb–MnSb system were found to exhibit large anisotropy. The low-temperature resistivity of the composites across the needles is four to five times that along the needles. With increasing temperature, the resistivity ratio drops by up to a factor of 2–3. This can be accounted for in terms of a geometric factor. The electrical conductivity of the composites is determined primarily by the MnSb phase, whose volume along the growth direction was considerably larger. According to magnetic measurements, the eutectic composites in the InSb–MnSb system are ferromagnets with a Curie temperature of ≃ 600 K.

Magnetic nanocomposites based on MnAs clusters embedded in a chalcopyrite host usually do not exhibit large magnetoresistance (MR) at room temperature, while pronounced effects are localized at very low temperatures. In the present work, we observed an appearance of large pressure-induced negative and positive MR at room temperature in the Zn0.1Cd0.9GeAs2 hybrid system containing 10% MnAs inclusions. With the applied pressure, a substantial modification of the electron transport from semimetallic to semiconducting type occurs, followed by a subsequent structural transition at P ≈ 3.5 GPa into almost metallic high-pressure phase. This picture is simultaneously supported by temperature-dependent and room temperature high-pressure transport measurements. Using a semiempirical expression, taking into account a spin-dependent scattering of charge carriers due to MnAs nanoclusters, as well as a two-band conductivity model, we have been able to partially describe the observed MR effects. The predominantly weak positive contribution at P = 1 GPa, which is well described in the framework of the proposed approach indicates the presence of spin-polarized charge carriers. Based on the two-band model calculations, a negative spin polarization was found at P ≥ 3 GPa that ascribed to a structural change of the matrix. As our results indicate, an emerging MR in the structural transition region is characterized by a complex behavior. In particular, the negative part of MR demonstrates a magnetic field dependence different than Δρ/ρ0 ∼ H2, suggesting the presence of unusual scattering mechanisms in magnetotransport. I. INTRODUCTION

Semiconductors of II-IV-V2 type with chalcopyrite structure have been studied for several decades. Due to advances in materials synthesis technologies, and doping with various elements, the possibilities of their application have expanded. In this paper, polycrystalline ZnSnSb2 + Mn was examined with the aim to explain the connection of its high free carrier concentration with the material structure and influence on optical properties. Two samples of Zn1-xMnxSnSb2 with different compositions (x = 0.027 and x = 0.076) and significant difference in carrier concentrations were analyzed. Their structural properties were examined by x-ray diffraction, optical microscopy, and AFM. The existence of several different phases - ZnSnSb2, ZnSb, SnSb, and small amounts of Sn and MnSb, as well as very complex microstructures, were registered. It was found that the high free carrier concentrations are caused by a large number of defects, especially zinc vacancies. Optical properties were analyzed using IR spectroscopy at room temperature. Based on the analysis of IR reflection spectra, the presence of plasmon - phonons interaction was registered. It was determined that three ZnSnSb2 phonons of B2 symmetry interact with plasma, which then leads to the change of their positions. A detailed analysis of this interaction provides insight into the behavior of some other material parameters. Also, vibration modes of ZnSb and SnSb phases were registered on the spectra. Knowledge of phonon behavior and their interaction with plasma is important for possible applications, especially as a thermoelectric material.

The ZnGeAs2–MnAs system is a eutectic-type system as determined by X-ray powder diffraction, DTA, and microstructure observation, with the eutectic coordinates: 61 mol % ZnGeAs2 mol %, 39 mol % MnAs, and Tm = 816°C. The eutectic is a lamellar eutectic as shown by microstructure examination. A characteristic feature of the system is a small mutual solubility of the components. Precision analysis of diffraction patterns enabled us to refine unit cell parameters for cubic and tetragonal ZnGeAs2 phases. MnAs in alloys is shown to consist of a hexagonal phase and a orthorhombic phase. ZnGeAs2 and MnAs alloys are ferromagnets (TC ~ 320 K). Their magnetization increases in response to increasing MnAs content.

The Zn3As2–MnAs system was studied by X-ray powder diffraction, differential thermal, and microstructural analyses. This system is of the eutectic type with the eutectic coordinates (30 wt % (50 mol %) Zn3As2, 70 wt % (50 mol %) MnAs, T melt = 815°C). The MnAs solubility boundary on the side of Zn3As2 is 10 wt %. Zn3As2 alloys containing more than 10 wt % MnAs are ferromagnetic with T c ~ 320 K. Their magnetization increases with increasing MnAs content.

Three self-assembled nanogranular composites based on MnAs ferromagnetic inclusions embedded in ZnSnAs 2 semiconductors with MnAs concentration 10, 20, 47 mol.% were synthesized. The samples were studied by X-ray, SEM, AFM, MFM and SQUID methods. It has been shown that the increasing of the MnAs concentration in composite leads to slightly increasing of the size of the magnetic inclusions. Their size depends mainly on the speed of the crystallization, but the shape of the inclusions depends on the type of the interaction between materials. The connection between equilibrium and non-equilibrium structure of the compounds has been demonstrated. Magnetic properties of the ZnSnAs 2 + MnAs samples show ferromagnetic phase transition with the Curie temperature having values from 313 K to 336 K, increasing as a function of the MnAs concentration in the nanocomposite. A small paramagnetic signal is observed at low temperatures due to individual Mn ions randomly distributed in the ZnSnAs 2 lattice. All our samples show only a narrow magnetic hysteresis loop except of the sample with 47 mol.% of MnAs, for which the coercive field increases to about 120 G. The carrier transport of the alloy shows significant influence of the MnAs clusters. All our samples have p-type conductivity with magnetotransport strongly influenced by the presence of the MnAs phase in the nanocomposite samples. The magnetoresistance (MR) of the alloy shows a complex behavior. The grain boundaries and MnAs clusters influence on the amplitude, sign, and temperature of MR.

The interest in thorough description of Zn 1– x Mn x GeAs 2 arises from its suitability for application in the field of non-linear optics. The room temperature far-infrared reflectivity spectra of single crystals Zn 1– x Mn x GeAs 2 , where 0 ≤ x ≤ 0.078, were measured in the spectral range from 80 cm −1 to 500 cm −1 . The spectra were analyzed by fitting procedure using a dielectric function which includes interaction between a plasmon and two different phonons. The detected phonons are in excellent agreement with the theoretical predictions. The MnAs cluster phonons are detected, as well.

In bulk samples of p-Cd1 − x Mn x GeP2, p-Cd1 − x Mn x GeAs2, and p-Zn1 − x Mn x GeAs2 at high hydrostatic pressures (P ≤ 9 GPa), the pressure dependences of the electrical resistivity and the volume change were studied. In all the studied samples, there were phase transitions accompanied by a volume jump. This suggested that the observed phase transition is a pressure-induced structural phase transition.

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.

The influence of the charge carrier concentration on the magnetic properties of GaSb-MnSb alloys is studied. The ferromagnetism of GaSb-MnSb films is caused by the presence of MnSb granules and manifests itself in both magnetometric measurements and the presence of an anisotropic magnetoresistance and the anomalous Hall effect. Electric conduction is executed by charge carriers (holes) in a GaSb matrix. The magnetization of clusters depends on stoichiometry and the concentration of Mn2+ and Mn3+ ions, which is specified by the film growth conditions. At high film growth temperatures, ferromagnetic clusters containing Mn2+ ions mainly form. At low growth temperatures, an antiferromagnetic phase containing Mn3+ ions forms.

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 requirements are formulated to be fulfilled by magnetic granular structures that have the giant magnetoresistance (GMR) in semiconductor-ferromagnet systems. AIIBIVC2V-Mn(CV), AIIICV-Mn(CV), and A3IIC2V-Mn(CV) semiconductor-ferromagnet systems are shown to be eutectic systems and to be promising for the preparation of granular structures with high magnetoresistance values. Magnetic granular structures have been prepared in Zn(Cd)GeAs2-MnP(As), Zn(Cd)3P(As)2-MnP(As), and (Al,Ga,In)Sb-MnSb systems and the origin of magnetoresistance in these systems is shown to be due to the structure of Mn(CV) ferromagnet clusters.

By the original method, using the sequential high-purity Mn and Sb metals evaporation, followed by annealing under high vacuum conditions, MnSb semiconductor films were synthesized. It is shown that the high chemical activity of nanostructured Mn and Sb films significantly reduces the manganese antimonide evaporation temperature. Films are p- type and have a high charge carriers mobility.

Eutectic GaSb + MnSb films ranging in thickness from 80 to 130 nm have been grown on sapphire substrates by pulsed laser deposition using mechanical droplet separation. The films were similar in composition to the ablation target, consisting of the eutectic GaSb-MnSb alloy. According to atomic force and electron microscopy data, the films were homogeneous, with p-type conductivity. Their electrical properties depended significantly on deposition conditions. The best films had a resistivity of 7 × 10−3 Ω cm, carrier concentration of 8.1 × 1019 cm−3, and carrier mobility of 102 cm2/(V s). Characteristically, the films had a negative magnetoresistance. Their magnetization curves showed saturation in a magnetic field of ∼1 × 10−1 T. According to the magnetic-field dependences, the coercive force in the films was within 3 × 10−2 T; that is, the films were soft magnets with a small domain size.

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.

The researching of dependence of magnetization from temperature T and magnetic field in the Bi2Fe0.128Te2.844Se0.145 single-crystal showed that it have spinglass-like state with freezing temperature Tf= 40 K. Its electric resistance up to 100 K is ~ 103 Ohm and decreases with the temperature increase. At T > 110 K electric resistance ~ 10-2 Ohm and magnetization is four times smaller than in spinglass-like state. It can be assumed from these results that this sample is topological insulator at T > 110 K and at small temperature, where it is spinglass-like, offers the breaking of the time reversal symmetry.

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 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.

Currently, complex ferromagnetic semiconductor systems are of significant interest due to their potential applicability in spintronics. A key feature in order to use semiconductor materials in spintronics is the presence of room temperature ferromagnetism. This feature was recently observed and is intensively studied in several Mn-alloyed II-IV-V2 group diluted magnetic semiconductor systems. The paper reviews the origin of room temperature ferromagnetism in II-IV-V2 compounds. In view of our recent reports the room temperature ferromagnetism in Mn-alloyed chalcopyrite semiconductors with more than 5 molar % of Mn is due to the presence of MnAs clusters. The solubility of magnetic impurities in bulk II-IV-V2 materials is of the order of a few percent, depending on the alloy composition. High values of the conducting hole - Mn ion exchange constant Jpd have significant value equal to 0.75 eV for Zn0.997Mn0.003GeAs2. The sample quality has significant effect on the magnetotransport of the alloy. The magnetoresistance of the alloy change main physical mechanism from spin-disorder scattering and weak localization for homogeneous samples to cluster-related geometrical effect observed for nanocomposite samples. The magnetoresistance of the II-IV-V2 alloys can be then tuned up to a few hundreds of percent via changes of the chemical composition of the alloy as well as a degree of disorder present in a material. [Projekat Ministarstva nauke Republike Srbije, br. III45003]

A set of physicochemical analysis methods showed that GaSb and MnSb form a eutectic at 41 mol % MnSb and Tmelt = 632°C. The eutectic is of the platelet type and has metallic conduction. The eutectic GaSb + MnSb is a composite ferromagnetic with a Curie temperature of ∼600 K. The behavior of the electrical resistance in a magnetic field is complex. At low magnetic fields up to 0.8 T, the resistance abruptly drops, and at high magnetic fields, it slowly increases. Such behavior occurs both at low temperatures (5 K) and at 300 K. The change of the trend in the resistance takes place at the magnetic field at which there is magnetization saturation in the magnetic field dependences. Such a dependence of the resistance on the magnetic field is explained by a change of the mechanism of scattering of charge carriers.

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%.

Optical properties of p-type Zn1−xMnxGeAs2 for 0 ⩽ x ⩽ 0.078 were investigated by Raman spectroscopy at room temperature. Phonons of ZnGeAs2 are experimentally determined and they are in excellent agreement with those theoretically predicted. Existence of MnAs clusters was confirmed in the sample with the highest concentration of Mn. MnAs was found in α and β phases and their vibrational frequencies are obtained experimentally. Plasmon – two different phonons interaction in Zn1−xMnxGeAs2 is registered and analyzed.

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.

Hydrostatic pressure studies of the isothermal magnetization and volume changes up to 7 GPa of magnetic composite containing MnP clusters in an insulating $\mathrm{CdGe}{\mathrm{P}}_{2}$ matrix are presented. Instead of alleged superparamagnetic behavior, a pressure-induced magnetization process was found at zero magnetic field, showing gradual enhancement in a low-field regime up to $H\ensuremath{\geqslant}5$ kOe. The simultaneous application of pressure and magnetic field reconfigures the MnP clusters with antiferromagnetic alignment, followed by onset of a field-induced metamagnetic transition. An unusual hysteresis in magnetization after pressure cycling is observed, which is also enhanced by application of the magnetic field, and indicates reversible metamagnetism of MnP clusters. We relate these effects to the major contribution of structural changes in the composite, where limited volume reduction by 1.8% is observed at $P\ensuremath{\sim}5.2$ GPa.

We present the studies of structural, transport and magnetotransport properties of [Formula: see text]Cd

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.