The paper studies the magnetic structure, electronic spectra, magnetic and conductive properties of composite films (CoFeB + SiO2) with different metal concentrations CoFe x = 41‒75 at

We studied the influence of a-Si and Ta2O5 interlayers on resistive switching processes, the nonlinearity of current–voltage characteristics in the induced low-resistance state, and conductivity mechanisms as a function of the current flowing through the investigated structures. The origins of the nonlinearity of the current–voltage characteristics were examined, and the limiting charge transport mechanisms in the fabricated structures were identified.

In this work, the concentration and angular dependences of the ferromagnetic resonance (FMR) linewidth ΔB and the resonance field Br of composite films (CoFeZr + Zr2O3) with granular and granular-percolation structures are obtained in the range of total concentration of Co and Fe metals x = 22–54 at

The influence of the composition of the gas medium in reactive ion-beam sputtering on the electrical properties of nitrogen-doped ZnO films was studied. It was found that, in the temperature range of 300-500 K, the electron transport in the experimental films occurs via variable-range hopping over localized states near the Fermi level. The parameters of ZnO were estimated according to the Mott model. It was established that the density g(EF) of localized states at the Fermi level is maximum in sputtering in a nitrogen medium and increases with increasing partial nitrogen pressure. For films deposited in a nitrogen–oxygen mixture, the density of states is lower, indicating the competing influence of oxygen and nitrogen on the formation of the defect structure.

The paper studies the temperature and frequency dependences of the real and imaginary components of the impedance of [(CoFeB + SiO2)/ZnO]50 multilayer films on sitall plates in the frequency range from 1 Hz to 1 MHz and in the temperature range from 120 to 420 K. Based on the measured specific surface electrical resistance, the multilayer films under study are divided into three groups with different types of conductivity: low, medium, and high. It is shown that at low frequencies up to 100 Hz and at temperatures above 260 K, the temperature behavior of the real part of the impedance of the planar structure multilayer film/sitall glass-ceramic is determined mainly by the behavior of the sitall plate. At high frequencies, starting from 1 kHz, the temperature behavior of the structure impedance in the entire studied temperature range of 120–420 K has the greatest difference; the higher the frequency and the lower the temperature, the greater these differences. For the planar structure multilayer film/sitall with a low composite layer conductivity, a decrease in the imaginary component of the impedance is observed with increasing temperature at frequencies above 10 kHz. An equivalent electrical circuit for the planar structure multilayer film/sitall is proposed. For effective control of the conductive and frequency properties of the planar structure multilayer film/sitall using alternating electric fields, it is proposed to use multilayer films with low conductivity.

Concentration and angular dependences of the parameters (line width and position) of ferromagnetic resonance (FMR) for CoTaNb/MgO composite films with metal alloy concentrations x = 0.27–0.72 were obtained in the work. Granular, granular-percolation structure and zigzag stripe magnetic structure for films with different x were detected. An increase in the FMR parameters with an increase in the angle from 0° to 90° between the constant magnetic field and the film plane with different x was observed. It was shown in the work that the behavior of the angular dependences strongly depends on the magnetic structure of the films, which have the greatest change in the region of transition from granular to granular-percolation structure with extended magnetic metallic microregions. The FMR method is a structure-sensitive method for scientific studies of the electromagnetic properties of thin magnetic composite films with granular and percolation structures and their combinations was demonstrated.

In this paper, we compare mechanical and thermoelectric parameters of Bi2Te2.5Se0.5 alloy prepared via zone recrystallization and extrusion. We have studied the effect of heat treatment on the ultimate strength and thermoelectric figure of merit of an n-type solid solution prepared via extrusion. Its thermoelectric parameters—Seebeck coefficient, electrical conductivity, and thermal conductivity—have been measured at room temperature and in the range 300–430 K, and its thermoelectric figure of merit ZT has been evaluated. The highest 350-K ZT value of the materials prepared via zone recrystallization is 1.0 ± 0.1, whereas the highest ZT value of the materials prepared via extrusion is 0.90 ± 0.1. Heat treatment in a vacuum thermostat at a temperature of 573 K for 24 h increased the highest ZT value of the materials prepared via extrusion to 0.96 ± 0.1 and their ultimate strength to 165 MPa.

Temperature dependences of magnetization of composite films (CoFeB + SiO2) with different concentrations of metal alloy x = 45–85 at

The optical and electrical properties of bismuth ferrite thin films obtained by high-frequency magnetron sputtering in an atmosphere of argon and oxygen (80%+20%) has been studied. Investigations of the optical properties have shown that for polycrystalline bismuth ferrite films the optical band gap is ~2.3 eV, which is in the range of given in the literature values. The dependences of the specific electrical conductivity on the magnitude of the electric field has been studied for the synthesized films. It has been established that the electrical conductivity does not depend on the electric field strength up to the value of E=2.1·10 6 V/m. The experimental results are discussed in terms of the model of charge carrier injection from aluminum electrode into the conduction band of bismuth ferrite. Keywords: electrical conductivity, strong electric fields, optical absorption coefficient, memristor effect.

Inelastic relaxation in amorphous tin oxide thin films obtained by ion-beam sputtering in an argon atmosphere were studied. The films retain an amorphous structure after annealing at temperatures below 623 K for 30 min and crystallization begins after annealing at 673 K with the formation of two phases, where the SnO2 phase predominates over the SnO phase. Annealing at 723 K for 30 min leads to a partial transition of the SnO crystalline phase to the SnO2 phase. The temperature dependence of internal friction revealed maxima at 585 K and 603 K, identified as beta relaxation maxima, as well as at 690 K, identified as alpha - relaxation maximum. It is assumed that the beta - relaxation maxima at 585 K and 603 K are associated with local hopps of oxygen atoms within the defect structure of SnO2 and with local hopps of tin atoms within the defect structure of SnO, respectively. The exponential increase in internal friction up to a temperature of 690 K in the alpha - relaxation region is associated with the diffusion of nonequilibrium vacancy-like defects of the amorphous structure below the glass transition temperature and equilibrium ones above the glass transition temperature. Estimates of the migration energy and formation energy of vacancy-like defects in amorphous tin oxide were made.

The electrical properties of Co-n(CoO)(100 -) (n) composite thin films obtained by ion-beam sputtering of a composite target in an argon atmosphere and a mixed atmosphere of argon and oxygen (98% Ar + 2% O-2) have been studied. It has been established that if oxygen is introduced into the deposition chamber, the position of the percolation threshold shifts towards lower concentrations of the metal phase. It is associated with the special morphology of the films, when small metal Co nanoparticles are located along the boundaries of larger CoO particles, as well as a decrease in the size of inclusions of the metal phase. Studies of the temperature dependences of the electrical resistivity of synthesized Co-n(CoO)(100 -) (n) films have shown that when the metal phase content is up to the percolation threshold the dominant mechanism of charge transfer in the temperature range of 80-140 K is the variable range hopping mechanism of conduction through localized states near the Fermi level, replaced by the nearest neighbors conductivity in the temperature range of 140-300 K. For beyond the percolation threshold Co-n(CoO)(100 -) (n) thin films, the conductivity is determined by a network of metal granules and is characterized by a positive temperature coefficient of electrical resistance.

The structural, electrical, magnetic, magneto-optical properties and magnetoresistance of {[(Co40Fe40B20)(34)(SiO2)(66)]/[ZnO]}(n) multilayer structures, where n = 50 is the number of bilayers (Co40Fe40B20)(34)(SiO2)(66) nanocomposite and ZnO have been studied. The thicknesses of (Co40Fe40B20)(34)(SiO2)(66) nanocomposite layers as well as ZnO spacers were varied in a wide range. The samples were synthesized by ion-beam sputtering onto glass ceramic substrates. The (Co40Fe40B20)(34)(SiO2)(66) composite have an amorphous structure and the semiconductor ZnO interlayers have a hexagonal crystalline structure with the p63mc symmetry group. The nanocomposite layers containing a ferromagnetic component far from the percolation threshold are in a superparamagnetic state. The presented in the paper data of magnetization, magneto-optical transverse Kerr effect and magnetoresistance indicates that long-range ferromagnetic order does not form down to 77 K both for references ZnO films and studied multilayers with thin and thick ZnO interlayers. An increase in the magneto-optical signal in multilayers compared to references (Co40Fe40B20)(34)(SiO2)(66) composite films has been detected at 1.2 eV. The magnetoresistance of {[(Co40Fe40B20)(34)(SiO2)(66)]/[ZnO]}(n) multilayers with thick (>32 nm) ZnO interlayers is lower than in reference (Co40Fe40B20)(34)(SiO2)(66) nanocomposite, while at thin ZnO interlayers magnetoresistance is significantly higher and reaches 12 % at temperatures of 77 & Kcy;. Possible mechanisms of ferromagnetic and antiferromagnetic ordering, enhancement of the magneto-optical response and magnetoresistance in {[(Co40Fe40B20)(34)(SiO2)(66)]/[ZnO]}(n) multilayer nanostructures are discussed.

High-temperature internal friction in an amorphous CuTi alloy is investigated. Exponential regions with different activation energies are observed on the dependence of internal friction on temperature on both sides of the glass transition temperature. An exponential increase in the background of internal friction with temperature in both sites is associated with the migration of vacancy-like defects in the amorphous structure under the influence of mechanical stresses, while frozen defects of constant concentration migrate to the glass transition temperature. After the transition to a state of thermodynamic equilibrium, the concentration the number of migrating defects increases exponentially. Based on the experimental results of measuring the high-temperature background, estimates of the activation energy of migration and the formation of vacancies of similar defects in the amorphous structure of the alloy under study are made.

The topological features of the formation of (Co40Fe40B20)15(LiNbO3)85 composite films deposited by ion-beam method on a metal electrode Cr/Cu/Cr has been investigated. The presence of a dielectric layer between the upper Cr layer and the CoFe–LiNbO3 film with a thickness of dox ≈ 15 nm has been established. The difference in the size of granules near the amorphous layer and in the volume of the film has been shown. A model of the formation of (Co40Fe40B20)x (LiNbO3)100 – x nanocomposite film at the initial stage of growth has been proposed. It has been shown that the formation of α-LiNbO3 layer on the chrome metal film surface is possible with the realization of island and layer-by-layer growth mechanisms for various phases of the composite.

The paper reveals the influence of Li, B and the composition of metal contacts on the processes of resistive switching in memristive structures M/NC/D/M. After field exposure in structures Cu/(Co50Fe50)x(LiNbO3)100–x/s-LiNbO3/Cu/sitall, Cu/(Co50Fe50)x(LiNbO3)100–x/d-LiNbO3/Cu/sitall and Cu/(Co40Fe40B20)x(SiO2)100–x/d LiNbO3/Cu/sitall at x < 13 was detected a residual voltage (up to 16 mV) due to the electromigration of Li ions, that leading to a “reversible” type of VAC hysteresis and instability of the time dependencies of induced resistive states. In the structures of Cu/(Co40Fe40B20)x(LiNbO3)100–x/s-LiNbO3/Cu/sitall, Cr/Cu/Cr/(Co40Fe40B20)x(LiNbO3)100–x/s-LiNbO3/Cr/Cu/Cr/sitall containing B, the residual voltage is reduced by formation of chemical compounds B with percolated Li atoms. When limiting the electromigration of Li ions, the main mechanism of resistive switching is the processes of electromigration of oxygen vacancies in the dielectric oxide layer. Suppression of residual voltage in the Cr/Cu/Cr/(Co50Fe50)x(LiNbO3)100–x/s-LiNbO3/Cr/Cu/Cr/sitall structure due to the introduction of a Cr buffer layer that does not dissolve Li leads to the absence of bipolar resistive switching in these structures.

The electrical properties of Con(CoO)100 – n composite thin films obtained by ion-beam sputtering of a composite target in an argon atmosphere and a mixed atmosphere of argon and oxygen (98

Composite films with compositions [(CoFeB)x+(SiO2)(1–x)+N2), x = 0,33–0,52] were obtained by ion-beam sputtering using metal alloy and dielectric targets in a nitrogen atmosphere. The thickness and content of atomic elements, and the concentration of metal alloy x composite films were found using a TESCAN MIRA3 electron microscope. Images of the magnetic phase contrast of the surface of composite films were obtained using magnetic force microscopy (Integra Prima atomic force microscope NT-MDT, Russia) with an MFM10 cantilever. Magnetic phase contrast images of x = 0,48–0,52 films were studied. All the composite films have granular and percolation structures, the volume ratio of these structures varies depending on x. The percolation structure of films with high concentrations x > 0,48 manifested in the presence of extended isolated areas (more than 1 μm) of the accumulation of metal granules. The temperature dependences of magnetic susceptibility, specific conductivity, and specific magnetic conductivity of the composite films with metal alloy concentrations x = 0,33–0,52 were studied in a temperature range of 2–400 K and in magnetic fields of 0 T, 1 T, and 5 T. All measurements of magnetic susceptibility and electrical resistance of the composite films in this temperature and magnetic field range were carried out at the center for diagnostics of functional materials for medicine, pharmacology, and nanoelectronics at St. Petersburg State University. In composite film No.1(x = 0,46) in the temperature range 100–300 K, the highest positive magnetic conductivity had a value of 1,2 at 200 K. The highest positive magnetic conductivity (about 1,2) was observed in composite granular films with small granule sizes. The results of temperature studies of the magnetic conductivity of the composites show that the ratio of positive and negative magnetic conductivity depends on the temperature of the film and on the concentration of the metal alloy x, which sets the ratio of the granular and percolation structures. Large negative magnetic conductivity (about –0,2) occurs in composite films No.3 and 5, the structure of which, along with the granular structure, includes extended (more than several micrometers) metallic areas of metal granules.

Optical and electrical properties of cobalt oxide thin films obtained by ion-beam sputtering in argon atmosphere and argon with the addition of oxygen (PAr=1.1·10-5 Torr) has been investigated in the work. Optical properties investigations showed that, for films of cobalt oxide obtained in argon atmosphere, the optical band gap is independent of the film thickness and is 3.24 eV, which is in the range of given in the literature for the CoO phase values. For cobalt oxide films obtained in mixed atmosphere of argon with the addition of oxygen, two direct optical transitions with energies of 1.45 and 2.1 eV were detected. The presence of two direct allowed optical transitions is associated with the variable valence of cobalt in the Co3O4 compound and the presence of two valence states Co2+ and Co3+. The dependences of specific electrical conductivity of the synthesized films on the magnitude of the electric field were studied. It was found that for all investigated samples, the electrical conductivity does not depend on the electric field strength up to the value of E=106 V/m. The nonlinearity of the dependence of specific electrical conductivity of the synthesized films on electric field strength at E>106 V/m is discussed in terms of the hopping conductivity model and the trap ionization model described by the Poole?Frenkel effect. Keywords: oxide semiconductors, optical absorption coefficient, electrical conductivity, strong electric fields.

It is found that (CoFeB + SiO2) composite films have a narrow spread of film surface protrusions at low concentrations of the metal alloy (x < 0.35), while a wider spread and smooth distribution of the protrusions are observed at the large concentration (x > 0.53). It is shown that the concentration dependence of the ferromagnetic resonance linewidth has a maximum at x = 0.45, due to the percolation structure of the films.

The structural, magnetic, and magnetoresistive properties of Cox(CoO)100-x thin film composites synthesized by ion-beam sputtering of a composite target in an argon and mixed atmosphere (argon + oxygen) has been studied. The experimentally determined percolation threshold was significantly lower than that for most of the studied previously nanocomposites: 12.2 at % Co and-8.3 at % Co for films fabricated in inert and mixed atmosphere, respectively. This is explained by the special morphology of the films when small metallic Co nanoparticles are located on the surface of larger CoO particles. A negative tunnel-type magnetoresistance reaching 2.4% in 9 kOe field at room temperature was found for composites with close to the percolation threshold Co content. The magnetoresistance is proportional to the square of magnetization and is characterized by hysteresis, which correlates well with magnetic hysteresis. Magnetic hysteresis with a coercivity of the order of 700 Oe is observed for dielectric compositions up to 4 at. % Co. A possible reason for this behavior, along with the special morphology, is the appearance of thin layers of antiferromagnetic oxide at the interface between Co nano particles and CoO particles, which causes a significant increase in magnetic anisotropy.