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In this study, we employed several experimental techniques to investigate structure and magnetic properties of poly(p-xylylene)–MnSb composites synthesized by low-temperature vapor deposition polymerization technique and MnSb films deposited at various temperatures. The presence of MnSb nanocrystallites in the studied films was verified by the results of X-ray diffraction, electron microscopy and Raman spectroscopy studies. The obtained data revealed the formation of Sb-rich sublayer with well-oriented Sb grains near the susbtrate, which seems to act as a buffer for the consequent poly(p-xylylene)–MnSb or MnSb layer growth. Increasing the polymer content results in qualitative change of surface morphology of studied films. At high polymer content the hybrid nanocomposite with MnSb nanoparticles embedded into poly(p-xylylene) matrix is formed. All investigated samples demonstrated detectable ferromagnetic response at room temperature, while the parameters of this response revealed a complex correlation with nominal composition, presented crystal phases and surface morphology of studied films. Estimated values of the Curie temperature of the samples are close to that of bulk MnSb.

Thin films of Dirac semimetal Cd3As2 about 100 nm thick made of single crystals of cadmium arsenide, prepared by direct fusion of the elements by vacuum–ampoule method, by vacuum–thermal sputtering/depostion have been studied. Temperature and magnetic field dependences of electrical resistance have been measured, which indicate the presence of a superconducting transition at a temperature from 0.2 to 0.6 K.

Thin films of solid solutions based on the three-dimensional Dirac semimetal Cd3As2 with the addition of manganese are investigated. Cd3 –xMnxAs2 films (x = 0, 0.05, and 0.1) 50–70 nm in thickness are formed on a glassceramic substrate using vacuum-thermal deposition from cadmium arsenide ingots doped by Mn and fabricated by direct alloying elements by the vacuum-cell method. The temperature and magnetic-field dependences of the resistance are measured and the transport parameters of the films under study are determined. Positive magnetoresistance of the characteristic shape corresponding to the contribution of the weak antilocalization effect is observed for films with x = 0 and 0.05. The contribution from the weak localization effect is observed at a higher Mn content (x = 0.1). This change in the quantum correction type as applied to topological semimetals points to reconstruction of the band structure and transition from the Dirac semimetal state into a trivial semiconductor phase, which corresponds to the critical Mn content xc ~ 0.07 in this case.

The vapor phase growth of Cd3As2—Zn3As2 (in the following (Cd1−x Znx)3As2 solid solutions process is described. The (Cd0,993 Zn0,007)3As2 solid solution single crystals were synthesized. Scanning electron microscopy and electron diffraction data suggest high crystalline quality of studied sample. Its structure and surface morphology, indicating the presence of growth nuclei and cleavage planes, were investigated. Giant anisotropic magnetoresistance and Shubnikov — de Haas oscillations were observed at low temperatures. Obtained results suggests that peculiarities of Dirac semimetal phase persist in (Cd1−x Znx)3As2 solid solution at low zinc content. At the same time, there are indications of some differences with initial Cd3As2 properties.

In this study, wide-angle X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy were employed to address the crystalline structure and morphology of poly(p-xylylene)–PbS nanocomposite thin films prepared by vapor deposition polymerization as well as their evolution upon thermal annealing. It was found that as-synthesized samples with different PbS contents demonstrate similar diffraction patterns that cannot be fully ascribed to a decrease in crystallite size, indicating distorted crystal structure of PbS nanoparticles compared to the bulk PbS. X-ray absorption spectroscopy reveals wide distribution of Pb–S bond lengths with a minimum value of 2.67 A, which can be attributed to the presence of molecular (PbS)n clusters in the studied films. It was shown that thermal annealing can be used to control the size of PbS nanoparticles and, as a consequence, optical properties of the composite films. The UV–vis absorption spectra demonstrate pronounced red shift of the absorption ...

We report a highly anisotropic magnetoresistance of (Cd0.993Zn0.007)3As2 single crystals, which have been synthesized by the vapor-phase growth. Scanning electron microscopy and electron diffraction data confirm the high crystalline quality of obtained samples. Studied samples exhibit specific features such as octahedral nuclei growth and step-like morphology of the surface formed by {112} planes. The giant anisotropic magnetoresistance and Shubnikov-de Haas oscillations have been observed at low temperatures. The results suggest the existence of the Dirac semimetal phase in (Cd1 −xZnx)3As2 solid solution with low zinc content. Thus, the observed magnetoresistance anisotropy is partially attributed to the chiral anomaly.

We studied the effect of Mn on the structure and properties of Cd3−xMnxAs2 crystals with x = 0–0.24, synthesized by direct fusion of high-purity elements. Obtained X-ray diffraction patters suggest that the incorporation of Mn promotes a structural phase transition from primary α-Cd3As2 (x = 0) phase to the α''– Cd3As2 (x = 0.24) phase, while at intermediate compositions both phases can coexist. In addition, the increase of Mn content results in the decrease of lattice cell parameters, which effectively saturates for x > 0.13. Microstructural, calorimetric and magnetometry studies suggest that at high Mn content (x = 0.24) secondary MnAs phase appears. Using obtained results, we estimated the solubility limit of Mn in Cd3As2 as x~0.13, which corresponds to the formation of ternary Cd3−xMnxAs2 compound where Cd atoms are partially substituted by Mn. Formation of ternary compound was also suggested by the results for Cd3As2 + MnAs composite systems, where we also observed the presence of CdAs2 phase, which is a byproduct of corresponding reaction. Additional studies suggested that the CdAs2 phase formation in composite system can be prevented if one uses the Cd3−xMnxAs2 compound instead of pure Cd3As2 as a matrix material.

The structure and conductivity of hybrid nanocomposite poly(p-xylylene) films containing iron nanoparticles are studied. The films are obtained by the method of polymerization on a surface from the gas phase, and the concentration of the filler is 4 and 11 vol %. According to the analysis of microphotographs of nanostructures obtained by transmission electron microscopy, the particles are distributed evenly (with a size in the nanometer range and a rather narrow distribution). Studies of the frequency dependence of conductivity show that the transport of the charge carriers is realized by the hopping mechanism with a jump length of ~3.5 nm.

We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition using the eutectic compound (GaSb)0.59(MnSb)0.41 as target for sputtering. For the studied films we have observed ferromagnetism and an anomalous Hall effect above room temperature, confirming the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggest that the films under study have a homogenous columnar structure in the bulk while MnSb inclusions accumulate near the surface. This is in good agreement with the high mobility values of charge carriers. Based on our data we conclude that the magnetic and magnetotransport properties of the films at room temperature are defined by the MnSb inclusions.

The relationship between structure, electrical and magnetic properties of thin poly( p -xylylene) - nickel nanocomposite films with Ni concentrations from 5 to 30 vol% was studied. It was found that metal concentration strongly affects size and oxidation state of the nanoparticles and composites morphology. At nickel concentration below 5 vol% the nanoparticles are oxidized to NiO and homogeneously distributed within fine-grained polymer matrix. An increase of Ni concentration up to 10 vol% results in the development of coarse-grained morphology with preferable localization of the nanoparticles at the boundaries of polymeric grains. And finally, in the composite films with nickel concentration above 20 vol%, the fine-grained morphology is observed again, but the nanoparticles are mainly metallic. Effect of the filler content on electrical and magnetic properties of the nanocomposites was elucidated showing that they are determined by percolation phenomenon with the threshold value of about 10 vol%. The well-pronounced magnetic hysteresis as well as ferromagnetic ordering were observed at Ni content above the percolation threshold. The diagrams of magnetic properties of these composites as a function of composition and temperature were elaborated. It was demonstrated that film annealing can be used to control magnetic properties of the composites and strongly enhance magnetoresistance.

The magnetotransport in Bi2Se3 thin films with magnetic Eu dopants is studied within the range of low applied magnetic fields. With the increase in the doping level, the saturation of the dephasing length on cooling is observed. This can be related to the existence of magnetic inclusions. The observed anisotropy of the magnetoresistance is qualitatively similar to the anisotropy characteristic of nonmagnetic Bi2Se3 films. Numerous similarities to the properties of pure Bi2Se3 films and some observed differences can be interpreted under the assumption of the local interaction of topologically nontrivial interface states with Eu-rich inclusions.

Magnetotransport in heterostructures with spatial separation of the Mn magnetic impurity and an InGaAs quantum well is studied. An analysis of the observed effect of weak localization using the Hikami–Larkin–Nagaoki formula leads to an anomalously small value (0.4) of the prefactor. Obtained data indicate that inelastic e–e scattering can be the dominant dephasing mechanism in the structures under study. Analysis of the conductivity and magnetoresistance indicates the dominant role of spin-dependent scattering at fluctuations in the magnetic subsystem, which is consistent with an increase in the amplitude of the negative magnetoresistance and an increase in the Drude conductivity as a result of cooling. The nature of the anomalous Hall effect in the studied structures is investigated; in particular, indications are obtained that there is the presence of a topological contribution at low temperatures.

Heterostructures with a GaAs/InGaAs/GaAs quantum well and aMn magnetic impurity layer separated from it, which have different conductivity types, are studied. At a Mn content not exceeding the amount corresponding to 0.5 monolayer of MnAs, a percolation cluster formed in the quantum well plane is not simply connected, but consists of metal drops separated by low-conductivity interspaces. Despite the absence of the simply connected conducting channel, Shubnikov–de Haas oscillations are observed in all studied systems, which are controlled by carrier properties in conducting drops, independent of Mn content. The estimate of drop sizes corresponds to theoretical values.

We report an experimental observation of superconductivity in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ thin films without application of external pressure. The films under study were synthesized by magnetron sputtering. Surface studies suggest that the observed transport characteristics are related to the polycrystalline continuous part of the investigated films with a homogeneous distribution of elements and the Cd-to-As ratio close to stoichiometric ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$. The latter is also supported by Raman spectra of the studied films where two pronounced peaks inherent to ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ were observed. The obtained x-ray diffraction patterns for studied films also correspond to the ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ lattice. The formation of a superconducting phase in the films under study is confirmed by the characteristic behavior of the temperature and the magnetic field dependence of the sample resistivity, as well as by the presence of pronounced zero-resistance plateaus in the $dV/dI$ characteristics. The corresponding ${H}_{c}\text{\ensuremath{-}}{T}_{c}$ plots reveal a clearly pronounced linear behavior within the intermediate temperature range, similar to that observed for bulk ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ and ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ films under pressure, suggesting the possibility of a nontrivial pairing in the films under investigation. We discuss a possible role of the sample inhomogeneities and crystal strains in the observed phenomena.

The magnetoconductivity of thin Bi2Se3 films covered by a protective Se layer and grown at (111) BaF2 substrates is studied. It is shown that the negative magnetoconductivity observed at low magnetic fields and caused by the effect of weak antilocalization, as well as the Shubnikov−de Haas oscillations at higher fields, is determined only by the magnetic field component perpendicular to the film plane. The obtained experimental results can be reasonably interpreted under the assumption that the studied films exhibit two-dimensional topologically protected electron states. Moreover, the contribution of these states to the total conductivity turns out to be the dominant one.

In $$_{x}$$ Ga $$_{1-{x}}$$ As/In $$_{y}$$ Al $$_{1-{y}}$$ As HEMT structures $${\updelta }$$ -doped by Si were grown by molecular beam epitaxy on InP substrate. We investigated the influence of the In content on the electron mobilities and effective masses in dimensionally quantized subbands. The electron effective masses were determined by the temperature dependence of the amplitude of the Shubnikov–de Haas effect at 1.6 and 4.2 K. We found that the more the In content in quantum well (QW), the less the electron effective masses. The mobilities are higher in HEMT structures with wider and deeper QW. The energy band diagrams were calculated by using Vegard’s law for basic parameters. The calculated band diagrams are in a good agreement with the experimental data of photoluminescence spectra.

We report the results of experimental and theoretical studies of Eu-doped Bi

The dependence of electrical and magnetic properties on structure of thin poly(p-xylylene) - nickel nanocomposite films with Ni concentrations from 5 to 30 vol.% was studied. It was found that metal concentration strongly affects size and oxidation state of the nanoparticles. Effect of the filler content on electrical and magnetic properties of the nanocomposites was revealed. These properties are determined by percolation phenomenon, with the percolation threshold value of about 10 vol.%. The well pronounced magnetic hysteresis as well as ferromagnetic ordering were observed at Ni content above the percolation threshold. The diagrams of magnetic properties of these composites as a function of composition and temperature were elaborated.

We have studied magnetoresistance and Hall effect of GaAs/InxGa1−xAs quantum wells with remote Mn impurity. Temperature and magnetic field dependencies of samples resistivity indicate several effects related to the magnetic subsystem. Shubnikov - de Haas oscillations indicate the presence of several types of regions in conduction channel with significantly different hole mobilities. We discussed the impact of magnetic impurities on quantum corrections to conductivity by comparing our results with the data for similar non-magnetic structures. Our results suggest that the presence of Mn atoms leads to the damping of quantum corrections in in the investigated structures.

Transport and magnetic properties of δ-Mn doped GaAs/InGaAs/GaAs quantum wells (QW) with various In content were studied at temperatures 4.2K≤T≤300K. Fluctuation potential (FP) appeared to be crucial for transport characteristics of structures under investigation. The magnetic percolation transition was observed at temperatureTpin the range 20 - 40K. TheTpdependence on the In content is nonmonotonic due to the peculiarities of free-carrier mediated exchange interaction mechanisms. The change of the anomalous Hall effect (AHE) sign with decreasing temperature was detected at temperatures close to theTp. The main reason of the AHE sign change is the variation of contributions of different AHE mechanisms (intrinsic and side-jump) caused by the reduction of spin-dependent scattering intensity with temperature decrease. We believe that our results are the experimental observation of the AHE intrinsic mechanism in 2D.

The influence of construction of the buffer layer and misorientation of the substrate on the electrical properties of In0.70Al0.30As/In0.76Ga0.24As/In0.70Al0.30As quantum wells on a GaAs substrate is studied. The temperature dependences (in the temperature range of 4.2 K < T < 300 K) and field dependences (in magnetic fields as high as 6 T) of the sample resistances are measured. Anisotropy of the resistances in different crystallographic directions is detected; this anisotropy depends on the substrate orientation and construction of the metamorphic buffer layer. In addition, the Hall effect and the Shubnikov–de Haas effect are studied. The Shubnikov–de Haas effect is used to determine the mobilities of electrons separately in several occupied dimensionally quantized subbands in different crystallographic directions. The calculated anisotropy of mobilities is in agreement with experimental data on the anisotropy of the resistances.

HEMT structures with In0.53Ga0.47As quantum well are synthesized using molecular-beam epitaxy on InP substrates. The structures are double-side Si δ-doped so that two dimensionally-quantized subbands are occupied. The effect of the central InAs nanoinsert in the quantum well on the electron effective masses m* and mobilities in each subband is studied. For experimental determination of m*, the quantum μ q and transport μ t mobilities of the two-dimensional electron gas in each dimensionally-quantized subband, the Shubnikov-de Haas effect is measured at two temperatures of 4.2 and 8.4 K. The electron effective masses are determined by the temperature dependence of the oscillation amplitudes, separating the oscillations of each dimensionally-quantized subband. The Fourier spectra of oscillations are used to determine the electron mobilities μ q and μ t in each dimensionally-quantized subband. It is shown that m* decreases as the InAs-nanoinsert thickness d in the In0.53Ga0.47As quantum well and electron mobilities increase. The maximum electron mobility is observed at the insert thickness d = 3.4 nm.

We study InSb:Mn polycrystals with different values of the Mn content. In these samples, two ferromagnetic phases have been found: MnSb nanoinclusions with TC ≈ 600 K and an InMnSb magnetic host with TC below 10 K. The magnetic field dependence obtained for the measured Hall resistance exhibits a nonlinear behavior within a wide temperature range. At high temperatures, such a behavior can be attributed to the existence of two types of charge carriers, namely, light and heavy holes. At temperatures below the Curie point of the InMnSb host, the anomalous Hall effect contributing to the nonlinearity of the Hall resistance has been observed. Ferromagnetic MnSb inclusions do not contribute to the anomalous Hall effect. They do not lead to any spin polarization of charge carriers owing to the Schottky barrier, which surrounds these inclusions and prevents their interaction with charge carriers. A method has been proposed for distinguishing the anomalous Hall component in the case where the Hall resistance includes a nonlinear contribution of a different nature.

For heterostructures with a GaAs/InGaAs/GaAs quantum well and a magnetic (Mn) δ-layer spatially separated from it (remote Mn δ-layer), the magnetic field and temperature dependences of the anomalous component of the Hall resistivity have been analyzed. The comparison with the temperature dependence of the longitudinal electrical resistance reveals three temperature ranges where three different mechanisms of the anomalous Hall effect are manifested. The reported results can be treated as experimental evidence of the essential role of the intrinsic mechanism of the anomalous Hall effect in a two-dimensional system.

Structural, magnetic and magnetotransport properties of (Bi$_{1-x}$Eu$_x$)$_2$Se$_3$ thin films have been studied experimentally as a function of Eu content. The films were synthesized by MBE. It is demonstrated that Eu distribution is not uniform, it enter quint-layers forming inside them plain (pancake-like) areas containing Eu atoms, which sizes and concentration increase with the growth of Eu content. Positive magnetoresistance related to the weak antilocalization was observed up to 15K. The antilocalization was not followed by weak localization as theory predicts for nontrivial topological states. Surprisingly, the features of antilocalization were seen even at Eu content $x$ $=$ 0.21. With the increase of Eu content the transition to ferromagnetic state occurs at $x$ about 0.1 and with the Curie temperature $\approx$ 8K, that rises up to 64K for $x$ $=$ 0.21. At temperatures above 1-2 K, the dephasing length is proportional to $T^{-1/2}$ indicating the dominant contribution of inelastic $e-e$ scattering into electron phase breaking. However, at low temperatures the dephasing length saturates, that could be due to the scattering on magnetic ions., 7 pages, 4 figuers

In this study, structure and magnetic properties of poly(p-xylylene)-MnSb nanocomposite films with different inorganic filler content were investigated. The thickness of all studied films was about 200-300 nm as determined by scanning electron microscopy. It was found that the filler concentration strongly affects surface morphology of the composite films. AFM revealed that the film with the lowest MnSb content has globular surface mophology, presumably formed by polymeric grains with small MnSb nanoparticles on their surface. Ferromagnetic hysteresis loop was observed for all studied films at room temperature with the saturation magnetization values correlating with the MnSb content.

We report the results of experimental and theoretical studies of Eu-doped Bi2Se3 thin films with extremely inhomogeneous distribution of magnetic component. The obtained electron microscopy images suggest that Eu atoms are concentrated within platelet-like nanoinclusions. The number of inclusions grows with the increase in Eu content, x. Moreover, at relatively high x values, the stacks of platelets (inclusions located one under another) become rather frequent. A comparative analysis of magnetic properties of the films under study reveals no pronounced changes of their temperature dependence with the increase in x, which, however, leads to the decrease in the average magnetic moment [Formula: see text] per Eu atom. A theoretical analysis of different mechanisms contributing to a possible magnetic ordering in the Eu-doped films demonstrates that at small distances (i.e. within a platelet) a dominant contribution is related to the RKKY interaction via electrons in the bulk, while the ordering at inter-platelet distances is governed by magnetic dipole-dipole interaction. The latter implies the antiferromagnetic ordering within the stacks of platelets explaining a drop of [Formula: see text] per Eu atom. We employ the model of a metallic spin glass to estimate the transition temperature, characterising the interaction within the ensemble of randomly distributed magnetic platelets. This estimate gives satisfactory agreement with the experiment, even if we take into account a finite film thickness, thus, neglecting the interaction anisotropy and including only the antiferromagnetism related to the stacking. While the overall contribution of interface Dirac electrons is damped in the systems under study, we argue that the obtained results can be used for the investigation of ultrathin films with analogous impurity profile, where this contribution should be clearly pronounced.

The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.

The Shubnikov - de Haas (SdH) effect at T=4.2 and 8.4 K and the Hall effect have been investigated in isomorphic In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As/InP quantum well with InAs inserts to the center of the quantum well. The structures were both- sides delta-doped by silicon. The effective mass m* was measured by SdH effect by a new method which allowed experimentally to determine m* in the every dimensionally quantized subband using the temperature dependence of the SdH effect amplitude. Central InAs inserts in a quantum well lead to a decreasing of m* by about 20% as compared with the uniform In0.53Ga0.47As lattice-matched quantum well. We also calculated the transport and quantum mobility of electrons in dimensionally quantized subbands using the SdH effect. The calculated and experimentally determined values are in a good agreement.

The electron effective masses m* in different dimensionally quantized subbands in InGaAs/InAlAs HEMT-structures have been measured by the Shubnikov – de Haas effect at two temperatures whose ratio was not equal to 2. The electron effective masses were found separately for the every subband. It was realized by digital bandpass filtering of the Shubnikov – de Haas oscillation to monochromatic oscillations corresponding to subbands. We obtained the dependence of m* in every subband on InAs content in quantum well.