Том 58, № 11 (2016)

This paper reports on the results of the investigation of a superconducting flux quantum bit (qubit) in the quasi-dispersive regime, where the frequency of a probe signal even though is lower than, but, nevertheless, close to the excitation frequency of the qubit. In this regime, in contrast to the known experiments, the interaction of the qubit with a waveguide leads not only to a shift of the resonance frequency, which is characteristic of the dispersive regime, but also to a significant broadening of the resonance line due to the spontaneous emission of the qubit. On the basis of the analysis of the amplitude–frequency characteristic of the transmission signal, this makes it possible to determine, under single-frequency excitation, the characteristic parameters of the qubit inductively coupled to the coplanar resonator.

An important role of the morphology of a superconducting layer in the superconducting spin-valve effect has been established. The triplet pairing induced by the superconductor/ferromagnet proximity effect has been experimentally investigated for samples CoO_x/Py1/Cu/Py2/Cu/Pb (where Py = Ni_0.81Fe_0.19) with a smooth superconducting layer. The optimization of the parameters of this structure has demonstrated a complete switching between the normal and superconducting states with a change in the relative orientation of magnetizations of the ferromagnetic layers from the antiparallel to orthogonal orientation. A pure triplet contribution has been observed for the sample with a permalloy layer thickness at which the superconducting spin-valve effect vanishes. A direct comparison of the experimental data with the theoretical calculation of the temperature of the transition to the superconducting state has been performed for the first time.

Selective measurements of the states are studied for a single quantum system, viz, a Josephson qubit, by a nonlinear oscillator operating in the mesoscopic regime in which the number of quanta during measurements is varied from a few dozen to several hundreds. The quantum Monte Carlo method is used to simulate the dissipative dynamics of the qubit–oscillator system and the process of measurements of the qubit states from the change in the number of oscillator quanta. It is shown that for π-pulses in the recording of qubit states, discrimination of states is possible in single realizations (measurements), while statistical projective measurements can be made for the prepared superposition state.

This paper presents the results of investigations of the high-frequency properties of multi-junction Josephson circuits based on high-temperature superconductors and the specific features of their use in voltage standards.

The parametric frequency division in a coplanar waveguide line with an integrated single-contact rf SQUID (Josephson oscillator) is discussed. It is assumed that the oscillator is excited by pump pulses whose carrier frequency can be a multiple of the plasma frequency of the oscillator. It is shown that the Josephson oscillator excited at the pump frequency can induce frequency division by emitting subharmonics that are multiples of the fundamental frequency (fractional resonances). Parameters for which parametric frequency transformation occurs are determined. The possible generalization of this effect to the quantum case in which correlated microwave photons (entangled photon states) can be generated is discussed.

The results of the micromagnetic simulation of forced oscillations of the magnetization in a system of two interacting microstrips located at an angle to each other have been presented. The ferromagnetic resonance spectra and the mode composition of resonant oscillations of the system have been investigated under the conditions of magnetostatic and exchange interactions between the microstrips. It has been shown that the magnetostatic interaction leads to the possibility of the excitation of in-phase and out-of-phase coupled oscillations of the magnetization of the microstrips. In the systems of exchange-coupled microstrips, there are intense resonances due to oscillations of the domain walls. The transformation of the ferromagnetic resonance spectrum and the change in the mode composition of resonant oscillations in different equilibrium configurations of the magnetization of the system have been discussed, as well as the conditions for the excitation of oscillations of different types depending on the direction of the microwave magnetic field.

This paper presents the results of theoretical and experimental investigations of the domain wall pinning in a planar ferromagnetic system consisting of a nanowire and four rectangular uniformly magnetized nanoparticles located at an angle to the nanowire axis. Based on the calculations of the interaction energy of the domain wall with stray fields of nanoparticles and the micromagnetic simulation, it has been demonstrated that, in this system, there are different variants of the domain wall pinning, which are determined by the relative orientation of the magnetic moments of nanoparticles and the magnetization of the nanowire. The possibility of the creation of magnetic logic cells based on the structures under consideration has been discussed.

The azimuthal anisotropy of the linear and nonlinear magnetooptical Kerr effect has been studied for a structure that is an ordered array with 420-nm-diameter pores in a 30-nm-thick permalloy film on a silicon substrate. The azimuthal anisotropy of the magnetooptical Kerr effect and the coercive force, corresponding to 4 m symmetry of a planar nanopore array, has been established experimentally. The measurements are accompanied with the numerical calculation of the anisotropic magnetization distribution in the structure at different orientations of the applied magnetic field.

The temperature and field dependences of the specific magnetization and magnetoresistance in heterostructures with a GaAs/Ga_0.84In_0.16As/GaAs quantum well and a δ-layer of atomic Mn in the barrier layer near the quantum well filled with holes are studied. A change in the resistance and magnetization behavior upon ordering of localized magnetic moments in the cap layer due to a change in the manganese ion distribution topology is detected.

The evolution of the antiferromagnetism vector of multiferroic BiFeO₃ during switching of its ferroelectric polarization by an electric field has been studied by numerical simulation in the framework of the phenomenological model for the magnetic anisotropy energy. Optimal variants have been found for the cut of electrosensitive BiFeO₃ layer, the deformation induced by a substrate, and the direction of applying electric field for the development of prototypes of new-generation marnetoresistive memory.

A hydrogen-containing ferroelectric triglycine sulfate (TGS) was comprehensively studied with an atomic force microscopy (AFM) and dielectric spectroscopy. The domain structure dynamics was in situ investigated with piezoresponse force microscopy (PFM) during heating and cooling the TGS crystal near phase transition. Relaxation dependencies of domain boundaries general perimeter and domain dimensions were obtained. TGS dielectric spectra measured at the frequency range from 10 to 10¹¹ Hz were analyzed on basis of significant contribution of conductivity into the dielectric response of ferroelectrics and a good agreement with the experimental data was received. It allows us to obtain more information about temperature dynamics of the domain structure.

Results of spectroscopic analysis of the optical second-harmonic (SH) generation in magnetic plasmonic structures comprised of iron garnet and periodic arrays of gold stripes are presented. It is shown experimentally that, in the region of the resonant excitation of a surface plasmon on the metal–magnetic dielectric interface, an increase in the SH intensity and an alternating modulation of the magnetic contrast for the SH, reaching 40%, are observed. The results are described in terms of a nonlinear Fano resonance.

Theoretical optimization of a quantum well heterostructure based on AlGaN solid solutions is implemented in order to attain the maximum charge carrier activation energy and the maximum exciton binding energy at a radiation wavelength of ~300 nm. An optimized structure sample with the radiative recombination dominating over the temperature range of 5 to 300 K and the room temperature internal quantum yield as high as 80% of the value measured at 5 K has been manufactured via plasma-assisted molecular beam epitaxy.

The magnetic properties of Co₄₅Pt₅₅ films deposited by electron-beam evaporation in vacuum have been studied. The measurements of the Faraday and Kerr magnetooptical effects confirm the presence of the easy-magnetization axis perpendicular to the Co₄₅Pt₅₅ surface. It is shown that the perpendicular magnetic anisotropy and the residual magnetization are retained at 300 K for a long time. The magnetic characteristics of the Co₄₅Pt₅₅ layer surface have been studied by magnetic force microscopy, and “circular” mobile magnetic structures have been detected. The spin light-emitting diodes based on In(Ga)As/GaAs heteronanostructures with Co₄₅Pt₅₅ contact layers were fabricated. These diodes emit circularly-polarized light in the absence of an external magnetic field.

Ferromagnetic single-crystal epitaxial Fe₃Si films and polycrystalline Fe₅Si₃ films are obtained on Si substrates by molecular-beam epitaxy with in situ control of the structure, optical, and magnetic properties. The results of the structural, magnetic, and optical measurements are discussed. The experimental data are compared to the results of the microscopic calculation of the spin-polarized structure, the permittivity, and the optical conductivity spectra.

The dependences of the electrical conductivity of europium monosulfide (EuS) polycrystals on temperature in the range 150–400 K and pressures to 620 MPa have been studied. It is shown that the electrotransfer is mainly performed due to a hopping mechanism.

The temperature dependence of the Hall coefficient of a single crystal of the p-Sb₂Te_2.9Se_0.1 solid solution grown by the Czochralski technique is studied in the temperature range 77–450 K. The data on the Hall coefficient of the p-Sb₂Te_2.9Se_0.1 are analyzed in combination with the data on the Seebeck and Nernst–Ettingshausen effects and the electrical conductivity with allowance for interband scattering. From an analysis of the temperature dependences of the four kinetic coefficients, it follows that, at T < 200 K, the experimental data are qualitatively and quantitatively described in terms of the one-band model. At higher temperatures, a complex structure of the valence band and the participation of the second-kind additional carriers (heavy holes) in the kinetic phenomena should be taken into account. It is shown that the calculations of the temperature dependences of the Seebeck and Hall coefficients performed in the two-band model agree with the experimental data with inclusion of the interband scattering when using the following parameters: effective masses of the density of states of light holes m_d1^*≈ 0.5m₀ (m₀ is the free electron mass) and heavy holes m_d2^*≈ 1.4m₀, the energy gap between the main and the additional extremes of the valence band ΔE_v ≈ 0.14 eV that is weakly dependent on temperature.

The results of ab initio calculations of the electronic structure, vibrational properties, and the magnetoelectric effect in the La₂CuTiO₆ crystal with double perovskite structure are presented. The lattice dynamics calculation shows the presence of unstable modes in the phonon spectrum of the high-symmetry cubic phase with space group \(Fm\overline 3 m\). Condensation of two most unstable modes belonging to the center and the boundary point X of the Brillouin zone leads to the formation of a nonpolar stable phase with space group P2₁/n. The calculation taking into account spin polarization shows that the magnetic ground state is E*-type antiferromagnetic with doubled magnetic cell and with the two spin-up and two spin-down configuration of magnetic moments of copper ions along the [010] crystallographic direction. Such ordering of magnetic moments leads to polar space group and polarization formation. The polarization magnitude is estimated as 71 μC/m².

The luminescence properties of needle-like crystals of diamond, obtained by selective oxidation of textured polycrystalline diamond films, are studied. Diamond films were grown by chemical vapor deposition from a methane–hydrogen mixture activated by a DC discharge. The spectra of photo- and cathodoluminescence and the spatial distribution of the intensity of radiation at different wavelengths are obtained for individual needle-like crystals. Based on the spectral characteristics, conclusions are made about the presence of optically active defects containing nitrogen and silicon impurities in their structure, as well as the significant effect of structural defects on their luminescence spectra.

Quartz plates placed in concrete are used to model the rock blasting procedure. Quartz fragments resulted from blasting are studied by small-angle X-ray scattering. Obtained grains in the quartz fragments are approximately 200–220 nm in size. The samples are discovered to contain low-dimensional (linear) components; the further the sample is from the explosion center, the coarser the grains are in it. Superlattice parameters of the studied fragments are estimated. It is suggested that domain boundaries in the sample quartz fragments are linear objects, such as dislocation walls.

Monodispersed spherical silica particles, including large mesopores (over 10 nm) and macropores (up to 100 nm) were obtained by chemical etching in an autoclave. A method for introducing globular protein myoglobin molecules into the pores is developed. The method of filling is based on a high adsorption capacity of the developed internal pore structure of the particles. The structure and adsorption properties of the materials are studied.

The quantitative analysis of the temperature dependence of the heat capacity of molecular crystals with chains of different lengths was performed using the theory of diffuse first-order phase transitions. The same chemical structure of the “core” of molecular crystals of {CH₃(CH₂)_nCH₃} normal paraffins, {COH(CH₂)_nCOH} diols, {CH₃(CH₂)_nCOH} normal alcohols, and {CH₃(CH₂)_nCOOH} saturated carboxylic and {COOH(CH₂)_nCOOH} dicarboxylic acids enabled the comparative analysis of phase transition parameters.

The magnetic-field induced orientational transition in helicoidal liquid-crystalline antiferromagnets representing compensated suspensions of magnetic nanoparticles in cholesteric liquid crystals is theoretically studied. The untwisting of a helicoidal structure and the behavior of mean magnetization as a function of the field strength and material parameters are investigated. It is shown that the magnetic subsystems in the field-untwisted ferronematic phase are not completely compensated, and the ferronematic phase is ferrimagnetic.

The study of the thermal characteristics of bulk nonferroelectric materials with low heat conductivity coefficient by the pyroelectrical rectangular thermal wave is shown to need the solution of the problem of the thermal conductivity for a three-layer system. The thermal characteristics of a paratellurite crystal with various crystallographic directions were studied. The heat conductivity coefficient is found to depend on the crystallographic direction.