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The nonlinearity of the gate–drain current–voltage characteristics in classical Schottky transistors and two-dimensional electron gas field-effect transistors based on AlGaAs/InGaAs/GaAs and InGaAs/GaAs compounds is analyzed. The carrier velocity-overshoot effect in the transistor channel is analyzed for various doping profiles of the structures under study.

Ge–Sb–Te (GST)-based PCM alloys are currently used in optical data storage. The crystallization of GST materials is the rate-limiting step for these devices, hence a deeper knowledge of the crystallization mechanism is crucial for insightful development of faster devices. In the present work, the diffraction patterns for GST-225 thin films are studied using the in situ Grazing Incidence X-ray Diffraction method upon heating. It is shown that initial amorphous film in the temperature range from 120 to 140 °C is crystallized into two phases-cubic GST-225 (Fm $${\bar{3}}$$ m), and trigonal GST-147 (P $${\bar{3}}$$ m1). The crystallized film is stressed and highly textured, and should be characterized by the value of the lattice parameters averaged over all crystallographic planes. The structural transition of GST-225 from cubic to trigonal phase begins at T > 180 °C. The appearance of large-scale inhomogeneities in GST-225 film at T ≥ 100 °C indicates that the process of rearrangement of atoms Ge, Sb, and Te in the as-deposited amorphous film begins long before the onset of crystallization.

Geometrical frustration arised in spin ices leads to fascinating emergent physical properties. Nowadays there is a wide diversity of the artificial structures, mimicking spin ice at the nanoscale and demonstrating some new effects. Most of the nanoscaled spin ices are two dimensional. Ferromagnetic inverse opal-like structures (IOLS) are among inspiring examples of the three-dimensional system exhibiting spin ice behaviour. However, a detailed examination of its properties is not straightforward. An experimental technique which is able to unambiguously recover magnetization distribution in 3D mesoscaled structures is lacking. In this work, we used an approach based on complementary exploiting of small-angle neutron diffraction technique and micromagnetic simulations. An external magnetic field was applied along three main directions of the IOLS mesostructure. Comparison of the calculated and measured data allowed us to determine IOLS magnetic state. The results are in good agreement with the spin ice model. Moreover influence of the demagnetizing field and vortex states on the magnetizing process were revealed. Additionally, we speculate that this approach can be also applied to other 3D magnetic mesostructures.

Ni- and Co-based inverse opals can be considered as a three-dimensional network of nanoobjects connected with each other by elongated crosspieces (legs). Inverse opals magnetic properties strongly depend on the legs aspect ratio which can be tuned during fabrication process. We study this dependence by means of micromagnetic simulations. We have found the range of ice-rule validity and studied limiting cases of high and low legs aspect ratio. We also investigate the value of the transverse magnetization component which should appear if the external field is applied perpendicular to one of the legs. Legs aspect ratio which corresponds to the maximal value of this component has been found. Finally, we calculate the dependence of the magnetic form factor on the external field for considered models. These results can be directly compared with experiment.

The impact of surfactant type on the structure organization of aqueous ferrofluids was considered based on the data of small-angle neutron scattering (SANS). The aggregates of different sizes and types were observed for magnetite magnetic nanoparticles of in heavy water stabilized by sodium oleate (SO) or dodecylbenzene sulphonic acid (DBSA). According to the surface tension measurements it was shown the significant difference of the critical micelle concentrations for SO and DBSA solutions. The observed structural difference of the aggregates in the ferrofluids was related to the behaviour of surfactant molecules in aqueous solutions including the structure and interaction parameters of micelles (micelle aggregation number, fractional charge, charge per micelle and surface potential, etc.) derived from the SANS analysis.

The structure of surface layers of thin metal inverse opals has been studied first by the grazing-incidence small-angle X-ray scattering technique. Contributions of the form factor and structure factor to the small-angle diffraction pattern have been separated using a numerical model of the scattering process. The complementary use of the small-angle X-ray scattering and grazing-incidence small-angle X-ray scattering techniques has provided independent information about the bulk and surface properties of the samples and allowed a type of defect in the investigated structures to be determined. The measurement results have been verified by atomic force microscopy.

We perform micromagnetic simulations of the magnetization distribution in inverse opal-like structures (IOLS) made from ferromagnetic materials (nickel and cobalt). It is shown that the unit cell of these complex structures, whose characteristic length is approximately 700 nm, can be divided into a set of structural elements some of which behave like Ising-like objects. A spin-ice behavior of IOLS is observed in a broad range of external magnetic fields. Numerical results describe successfully the experimental hysteresis curves of the magnetization in Ni- and Co-based IOLS. We conclude that ferromagnetic IOLS can be considered as the first realization of three-dimensional artificial spin ice. The problem is discussed of optimal geometrical properties and material characteristics of IOLS for the spin-ice rule fulfillment.

Electric and magnetic tuning of phase, frequency, and delay time of electromagnetic-spin waves in thin-film layered multiferroic structure (metal-dielectric gap-ferroelectric material-hexaferrite-dielectric substrate) is numerically simulated. The results are used to demonstrate prospects for application of layered multiferroic hexaferrite-ferroelectric structures in the construction of basically new devices for generation and processing of microwave signals under dual (electric and magnetic) tuning of the working characteristics in the subterahertz frequency range.

A general theory of the spectrum of normal waves propagating in magnetic structures with periodically modulated parameters has been developed. Based on the method of tensorial Green’s functions, spin-wave mode approach, and Floquet-Bloch theorem, a general form of the dispersion relation has been obtained for dipole-exchange spin waves propagating in a one-dimensional magnonic crystal formed by an arbitrary spatially periodic modulation of all magnetic and geometric parameters in the Maxwell’s equations and the Landau-Lifshitz equation. An original method has been proposed for taking into account an arbitrary profile of the modulation of the chosen parameters. The efficiency of the presented theory has been demonstrated using a simple example of the description of an experimental spectrum of a dynamic magnonic crystal.

An experiment on small-angle polarized-neutron diffraction by a two-dimensional spatially ordered array of nickel nanowires embedded in a porous anodic alumina matrix is discussed. The contributions of nonmagnetic (nuclear) structures and nuclear magnetic interference indicating the correlation between magnetic and nuclear structures are discussed. Magnetic scattering is two orders of magnitude smaller than nuclear scattering and, hence, turns out to be weakly distinguishable. The ordered magnetic composite nanostructure of a sample leads to strong interaction between the neutron wave and the structure itself, which, in turn, implies a twofold (miltiple scattering) nuclear scattering process. Nuclear magnetic interference scattering must be analyzed allowing for twofold scattering conditions, which substantially distorts the intensity distribution of the interference contribution of first-order diffraction peaks.

Formation of artificial opal films by a vertical deposition method was in situ studied using the grazing incidence X-ray diffraction technique. Monodisperse spherical polymethyl methacrylate particles (200 nm in diameter) were deposited on the polished Si substrate from an aqueous suspension. The ordering of particles on a fixed area of the substrate located in turn in the bulk suspension under the meniscus and in the air was continuously monitored by the X-ray scattering upon moving the meniscus down owing to evaporation of the solvent. The triple air-liquid-solid phase boundary, i.e. the top line of the meniscus, is identified as the most probable location of the crystallization process. The analysis of observed Bragg reflections and the particle form-factor indicates that the obtained artificial opal-like structures are composed of the spheres arranged in a close-packed hexagonal layers parallel to the substrate. The characteristic correlation length along the normal to the substrate of 550 ± 100 nm is obtained from the half full width of Bragg peaks.

Magnetization hysteresis loops of a three-dimensional nanoscale analog of spin ice based on the nickel inverse opal-like structure (IOLS) have been studied at room temperature. The samples are produced by filling nickel into the voids of artificial opal-like films. The spin ice behavior is induced by tetrahedral elements within the IOLS, which have the same arrangement of magnetic moments as a spin ice. The thickness of the films vary from a two-dimensional, i.e., single-layered, antidot array to a three-dimensional, i.e., multilayered, structure. The coercive force, the saturation, and the irreversibility field have been measured in dependence of the thickness of the IOLS for in-plane and out-of-plane applied fields. The irreversibility and saturation fields change abruptly from the antidot array to the three-dimensional IOLS and remain constant upon further increase of the number of layers $n$. The coercive force ${H}_{c}$ seems to increase logarithmically with increasing $n$ as ${H}_{c}={H}_{c0}+\ensuremath{\alpha}ln(n+1)$. The logarithmic law implies the avalanchelike remagnetization of anisotropic structural elements connecting tetrahedral and cubic nodes in the IOLS. We conclude that the ``ice rule'' is the base of mechanism regulating this process.

Magnetic properties of spatially ordered arrays of interacting nanofilaments have been studied by means of smallangle diffraction of polarized neutrons. Several diffr action maxima or rings that correspond to the scat� tering of the highly ordered structure of pores/filaments with hexagonal packing have been observed in neu� tron scattering intensity maps. The interference (nuclearmagnetic) and pure magnetic contributions to the scattering have been analyzed during the magnetic reversal of the nanofilament array in a field applied per� pendicular to the nanofilament axis. The average magnetization and the interference contribution propor� tional to it increase with the field and are saturated at H = H S. The magnetic reversal process occurs almost without hysteresis. The intensity of the magnetic contribution has hysteresis behavior in the magnetic reversal process for both the positive and negative fields that form the field dependence of the intensity in a butterfly shape. It has been shown that this dependence is due to the magnetostatic interaction between the filaments in the field range of H ≤ HS. A theory for describing the magnetic properties of the arrays of interacting ferro� magnetic nanofilaments in the magnetic field has been proposed.

The distribution of the scattering intensity in the reciprocal space for natural and artificial opals has been reconstructed from a set of small-angle X-ray diffraction patterns. The resulting three-dimensional intensity maps are used to analyze the defect structure of opals. The structure of artificial opals can be satisfactorily described in the Wilson probability model with the prevalence of layers in the fcc environment. The diffraction patterns observed for a natural opal confirm the presence of sufficiently long unequally occupied fcc domains.

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic nickel nanowires embedded into Al 2 O 3 matrix have been studied using polarized small-angle neutron scattering. The small-angle diffraction pattern exhibits many diffraction peaks, which corresponds to the scattering from highly correlated hexagonal structure of pores and magnetic nanowires. Magnetic contribution to the scattering has complex behavior and cannot be explained without taking into account stray fields located between magnetized nanowires.

Some peculiarities of heat and mass transfer processes in units of lithium bromide thermotransformers as applied to the problem of development of new-generation refrigerating machines and thermal pumps are presented.

The magnetic and structural properties of two-dimensional spatially ordered systems of ferromagnetic nickel nanowires embedded into an Al2O3 matrix have been studied using polarized small-angle neutron scattering (polarized SANS). We measured the total (nuclear and magnetic) scattering I(q) as a polarization-independent scattering, the field-dependent scattering as IH(q) = I(q, H) − I(q, 0), where H is the magnetic field, and the nuclear-magnetic interference as a polarization-dependent (P) scattering ΔI(q, P). A typical scattering pattern is composed of the diffuse small-angle scattering and the Bragg peak. It is shown that the introduction of Ni into the matrix does not change the position of the Bragg peak but results in an increase of the scattering intensity both in the small-angle region and at the Bragg positions. An external magnetic field was applied perpendicular or parallel to the long dimension of the nanowires in order to reveal the anisotropic properties of the magnetic system. It is shown that, firstly, the magnetic-field-dependent scattering IH(q) provides new and principally different information as compared with the interference term ΔI(q). Secondly, two contributions to the interference term ΔI(q) (ascribed to the diffuse scattering and to the diffraction peaks) have different signs indicating different origins of the scattering objects. Thirdly, polarized SANS gives a detailed picture of the magnetization process, which could not be obtained by methods of standard magnetometry.

In the present study we report synthesis and investigation of the magnetic iron nanowire arrays in the mesoporous silica thin films. The films were deposited on SiC/Si(100) substrate by spin-coating technique, enabling one to obtain all mesopores parallel to the substrate surface and aligned radially by centrifugal force. Very high level of local alignment (90% on 2 cm2) of the pores was proved by small angle X-ray scattering and neutron reflectivity. Magnetic iron nanowires were synthesized in the mesoporous silica channels by intercalation of a hydrophobic iron compound into a hydrophobic part of the silica–surfactant composite followed by decomposition of the complex and additional crystallization of iron in hydrogen flow. Nanocomposites were studied by TEM, ED, SAXS, BET, BJH and neutron reflectometry. It was found that an ordered structure preserves after the chemical modification, while iron nanowires uniformly fill porous structure, making this system highly promising for high-density data recording media.

The structure of inverse opal crystals based on nickel was probed on the mesoscopic and atomic levels by a set of complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale face-centered-cubic (fcc) ordering of spherical voids in the inverse opal-like structure with unit cell dimension of 750±10nm. The diffuse scattering data were used to map defects in the fcc structure as a function of the number of layers in the Ni inverse opal-like structure. The average lateral size of mesoscopic domains is found to be independent of the number of layers. 3D reconstruction of the reciprocal space for the inverse opal crystals with different thickness provided an indirect study of original opal templates in a depth-resolved way. The microstructure and thermal response of the framework of the porous inverse opal crystal was examined using wide-angle powder x-ray diffraction. This artificial porous structure is built from nickel crystallites possessing stacking faults and dislocations peculiar for the nickel thin films.

Polarized neutron reflectometry is used to investigate SiO2(Co) granular films (70 at% of Co nanoparticles in SiO2 matrix) deposited on Si and GaAs substrates. The aim of the study is to compare magnetization depth profiles in two systems: in SiO2(Co)/GaAs heterostructure which shows at room temperature giant injection magnetoresistance (IMR) with the system SiO2(Co)/Si which reveals almost no IMR effect. We found that at room temperature and at the same value of external magnetic field mean magnetization in the SiO2(Co)/GaAs sample is much higher than in the case of SiO2(Co)/Si. We also demonstrate that magnetic scattering length density, and hence, magnetization profile strongly depends on the substrate. We show that SiO2(Co)/Si heterostructure is ferromagnetically ordered within the temperature range between 120 and 460 K what could explain a weak IMR.

Polarized small-angle neutron scattering (SANS) technique is used to study spatially ordered one-dimensional (ID) magnetic nanowires. In our experiments a typical q-dependence consists of the diffuse small-angle scattering and the Bragg peak corresponding to the scattering on the regular structure of the porous matrix. We measured the total (nuclear and magnetic) scattering and the nuclear–magnetic interference as a polarization-dependent part of the scattering. The field- and temperature-dependent scattering intensity is extracted as I{H,T}(q)=I(q, H, T)−I(q, 0, TR). It is shown that the magnetic scattering I{H,T}(q), obtained from the polarization-independent part, brings new and principally different information as compared to the interference term ΔI(q). We present Co embedded into mesoporous aluminosilicate matrices (MAS) as an example of investigations of the spatially ordered one-dimensional magnetic nanosystems.

The evolution of the magnetic structure for an inverse opal-like structure under an applied magnetic field is studied by small-angle neutron scattering. The samples were produced by filling the voids of an artificial opal film with Co. It is shown that the local configuration of magnetization is inhomogeneous over the basic element of the inverse opal-like lattice structure (IOLS) but follows its periodicity. Applying the “ice-rule” concept to the structure, we describe the local magnetization of this ferromagnetic three-dimensional lattice. We have developed a model of the remagnetization process predicting the occurrence of an unusual perpendicular component of the magnetization in the IOLS which is defined only by the direction and strength of the applied magnetic field.

Investigations of microwave properties of Ni-based inverse ferromagnetic opal-like film with the [111] axis of the fcc structure along the normal direction to the film have been carried out in the 2--18 GHz frequency band. We observed multiple spin wave resonances for the magnetic field applied perpendicular to the film, i.e., along the [111] axis of this artificial crystal. For the field applied in the film plane, a broad band of microwave absorption is observed, which does not contain a fine structure. The field ranges of the responses observed are quite different for these two magnetization directions. This suggests a collective magnetic ground state or shape anisotropy and collective microwave dynamics for this foam-like material. This result is in agreement with SQUID measurements of hysteresis loops for the material. Two different models for this collective behavior are suggested that satisfactorily explain the major experimental results.

Conclusions To summarize, in this chapter diffraction of light and x-rays on opal-like structures is considered. New methodological approaches to collection, processing, and interpretation of experimental data are presented. In particular, a novel representation of the light diffraction data in the “incident angle–registration angle” (θ, Θ) coordinates is shown to be an effective tool of data analysis. This representation allows one to easily distinguish the reflections originating from 2D diffraction from the ones governed by 3D Bragg diffraction. In addition, structural disorder becomes apparent in the (θ, Θ) representation. It is also demonstrated that the immersion spectroscopy method can be used to selectively switch diffraction reflections. This phenomenon is caused by inhomogeneity of the a-SiO2 particles that form synthetic opals. Furthermore, it is demonstrated that microradian x-ray diffraction is a powerful technique that is able to reveal the dominating structure and the presence of disorder in opallike structures. Short acquisition times, modern 2D detectors, and progress in computing techniques make 3D reconstructions of reciprocal space routinely available. This method provides extremely valuable information on the real structure of mesoscopic materials that cannot be easily obtained by other analytical approaches. K13299_

Inverse photonic nickel-based crystal films formed by electrocrystallization of metal inside the voids of polymer artificial opal have been studied using the microradian X-ray diffraction. Analysis of the diffraction images agrees with an face-centred cubic (FCC) structure with the lattice constant a0 650 10 nm and indicates two types of stacking sequences coexisting in the crystal (twins of ABCABC... and ACBACB... ordering motifs), the ratio between them being 4:5 The transverse structural correlation length Ltran is 2.4 0.1 μm, which corresponds to a sample thickness of 6 layers. The in-plane structural correlation length L long is 3.4 0.2 μm, and the structure mosaic is of order of 10°.

The structural and magnetic properties of nickel inverse opal photonic crystal have been studied by complementary experimental techniques, including scanning electron microscopy, wide-angle and small-angle diffraction of synchrotron radiation, and polarized neutrons. The sample was fabricated by electrochemical deposition of nickel in voids in a colloidal crystal film made of 450 nm polystyrene microspheres followed by their dissolving in toluene. The microradian small-angle diffraction of synchrotron radiation was used to reveal the opal-like large-scale ordering proving its tendency to the face-centered-cubic fcc structure with the lattice constant of 65010 nm. The wide-angle x-ray powder diffraction has shown that nanosize fcc nickel crystallites, which form an inverse opal framework, have some texture prescribed by principal directions in inverse opal on a macroscale, thus showing that the atomic and macroscopic structures are correlated. The polarized small-angle neutron scattering is used on the extreme limit of its ability to detect the transformation of the magnetic structure under applied field. Different contributions to the neutron scattering have been analyzed: the nonmagnetic nuclear one, the pure magnetic one, and the nuclear-magnetic interference. The latter in the diffraction pattern shows the degree of the spatial correlation between the magnetic and nuclear reflecting planes and gives the pattern behavior of the reversal magnetization process for these planes. The field dependence of pure magnetic contribution shows that the three-dimensional geometrical shape of the structure presumably leads to a complex distribution of the magnetization in the sample.

Ultramicrotomy was used to prepare a cross-section of shell-like amorphous SiO2 spherical particle synthesized by the multistage Stöber method which allowed performing first direct observations of the hierarchical structure of the SiO2 particle by transmission and scanning electron microscopy. The presence of primary, secondary and tertiary particles forming the inner structure of SiO2 spheres was established. The use of the small angle scattering of neutrons and synchrotron radiation techniques has enabled to define the size of the primary particles, the fractal parameters of their surface and the bulk density of the SiO2 spheres.

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic cobalt nanowires embedded into Al2O3 matrix have been studied using polarized small-angle neutron scattering. The small-angle scattering pattern exhibits many diffraction peaks (up to the third reflection order), which corresponds to the scattering from highly correlated hexagonal structure of pores and magnetic nanowires. A comprehensive analysis of contributions to the scattering intensity, including nonmagnetic (nuclear) contribution, magnetic contribution depending on the magnetic field, and nuclear-magnetic interference indicating the correlation between the magnetic and nuclear structures was carried out. A detailed pattern of the remagnetization of an ordered array of the magnetic nanowires has been obtained. It has been illustrated that polarized neutron scattering provides unique information inaccessible by the standard magnetometry techniques.

Changes of electrokinetic properties of cell nuclei and the quantity of granules of heterochromatin located near the nuclear envelope in nuclei of human buccal epithelium cells were studied under the influence of electromagnetic fields in vitro. Irradiation of cells was realized by means of a semiconductor generator of millimeter radiation (wavelength 7.1 mm, frequency 42.2 GHz), the Yav-1 apparatus for extremely high frequency therapy. It was shown that irradiation of cells induced a decrease in electric charge of native human buccal epithelium cell nuclei and an increase in chromatin condensation in nuclei. The observed effects depend on irradiation dose and individual peculiarities of donors.

In this work diffraction of light and x-rays (XRD) on opal-like structures (OLS) is considered. New methodological approaches to collection, processing and interpretation of experimental data are presented. The microradian XRD reveals the type and degree of imperfection of opal-like structures. It was shown that the OLS ordered in the twinned face centered cubic (FCC) structures with the lattice constant of 835 ± 10 nm but also with clear tendency to the random hexagonal close-packed (RHCP) structure along the [111] axis. A novel representation of the light diffraction data in the “incident angle — scattered angle” coordinates (θ, Θ) allows one to easily distinguish the reflections originating from 2D diffraction from the ones governed by 3D Bragg diffraction. Structural disorder becomes apparent in the (θ, Θ) representation, as well. In addition, it was demonstrated that the immersion spectroscopy method can be used to selectively switch diffraction reflections. This phenomenon is caused by optical inhomogeneity of the SiO 2 particles that form opal-like crystals.