Vol 60, No 11 (2018)

Abstract—It is demonstrated in the (pseudo)spin S = 1 formalism that the structure of antiphase domain boundaries in the phase of charge ordering of a mixed-valence system of the Cu^1+, 2+, 3+ “triplet” type in cuprates on a two-dimensional square lattice depends to a considerable extent on on-site correlation parameter U. The results of computer modeling on large square lattices illustrate the change in the boundary structure (from a homogeneous monovalent nonconducting structure of the Cu²⁺ type to a filamentary superconducting one) induced by a relatively small variation of positive U values.

Abstract—The development of a new “master mask” method for the manufacture of planar structures based on a high-temperature YBCO superconductor is considered. The method involves the creation of a mask on the blank substrate and, upon deposition of YBCO, the superconducting elements are formed in preset local windows of the mask with isolation regions formed between them. Such growth conditions allow the fabrication of micron-size superconducting elements with excellent electrophysical parameters and a smooth su-rface. The influence of the parameters of the master mask of amorphous cerium oxide on the isolating properties of the resulting isolation regions during the fabrication of planar structures on sapphire and cubic zirconia substrates with epitaxial cerium oxide sublayers has been studied.

Abstract—Based on the Ginzburg–Landau theory, the dependence of the threshold energy δF_thr of formation of a phase slip center from the current for a superconducting two-band bridge has been calculated. It has been found that, in the case of sufficiently long bridges and a weak interband Josephson coupling, there is a range of currents at which fluctuation transition from the state of the zero interband phase difference to the states with a phase soliton is possible, which manifests itself in a considerable decrease in the threshold energy δF_thr, and a fluctuation change in the number of phase solitons in the bridge. In the case of a strong interband coupling, no fluctuation formation of phase solitons occurs and the dependence δF_thr(I) tends to the expression obtained earlier by Langer and Ambegaokar for a single-band superconductor.

Abstract—The temperature dependences of the Hall effect of an electron-doped Nd_2 – xCe_xCuO_4 + δ superconductor have been studied at the antiferromagnet–superconductor quantum phase transition boundary (0.135 ≤ x ≤ 0.15) in conducting CuO₂ planes and in the direction perpendicular to the CuO₂ plane. The hall coefficient between the conducting planes has been found be two orders higher than that in the conducting planes over entire temperature range, which is due to the incoherent character of the charge carrier transfer in the direction of axis c.

Abstract—The effect of current and magnetic field on the transition to the superconducting state in niobium nitride thin films has been studied. The critical current dependences of the films on the temperature and magnetic field in the transition region have been determined. Within the framework of models of a normal domain and quasiparticle heating during viscous flow of a magnetic flux, the functional dependences of the critical current have been determined in close vicinity of the superconducting transition temperature. Using the theory of electron heating, we have determined the time of the electron energy relaxation. We also estimated the electron-phonon and the electron-electron inelastic scattering times, the diffusion coefficient of electrons, and heat transfer coefficient.

Abstract—An oscillator based on the distributed tunnel superconductor-insulator-superconductor junction with an ultrawide operating bandwidth of up to 100% of the central frequency seems to be a promising type of directional source of continuous electromagnetic radiation in the terahertz frequency range. In this paper, we propose a scheme of a terahertz oscillator integrated on a single microchip with a transmitting lens antenna with the slot structure in a 200-nm Nb film to radiate the signal into the open space. We also proposed and numerically simulated several designs of a planar slot antenna matched (in the input) with a Josephson oscillator and (in the output) with a silicon elliptical lens. The obtained results of the matching of the oscillator output power with the antenna of various designs operating in four frequency ranges: 250–410, 330–570, 380–520, and 420–700 GHz are presented. The antenna beam patterns and impedances are calculated as well.

Abstract—Spin light emitting diodes (spin-LEDs) containing (Ga,Mn)As ferromagnetic layers are fabricated based on InGaAs/GaAs heterostructures and studied. We achieve increases in the operating temperatures of our spin-LEDs by subjecting the surface of the structures, prior to depositing an ohmic metal contact, to pulsed laser annealing. The fabricated devices produce circularly polarized electroluminescence when placed in an external magnetic field. The temperatures at which circularly polarized electroluminescence is still observed is raised from 30 K for unprocessed structure to 110 K for laser-annealed structures. The observed effect is linked to an increase in the Curie temperature of the (Ga,Mn)As layer as a result of laser impact.

Abstract—In this paper, we present studies of the characteristics of quantum-cascade lasers with a generation wavelength in the region of 8 μm at high temperatures of up to + 65°C. The characteristic temperatures of the temperature dependences of the threshold current and the differential efficiency are determined. Spectral studies showed the presence of two generation lines with a short wavelength of ~7800 nm and a long-wave wavelength of ~8100 nm. The observed competition between the short-wave and long-wave generation lines leads to a nonmonotonic character of the dependence of the radiation intensity on the pump current.

Abstract—Magnetic force microscopy has been used to study the distribution of the magnetization in permalloy microparticles with a configurational anisotropy. The triangular particles with different degrees of concavity of the lateral sides have been studied. An analysis of the results enables us to state that the particles can be in several quasi-homogeneous stable states. It is shown that the particle magnetization reversal can occur both stepwise and also via an intermediate state in the dependence on the particle orientation. It is demonstrated that the quasi-homogeneous magnetization orientation in a particle can be changed by a magnetic-force microscope probe.

Abstract—A technique of measuring the rotation of the light polarization plane in pulsed magnetic fields with strength up to 40 T with a sensitivity of  0.1° is proposed. The Faraday effect has been studied in films of diluted ferrites—garnets (Lu,Bi)₃(Fe,Ga,Al)₅O₁₂ in the temperature range from room temperature to 78 K, including the vicinity of the magnetic moment compensation temperature. The transition to the noncollinear phase in the magnetic phase diagram is shown to occur at a magnetic field strength higher than 30 T at room temperature, and the threshold transition field tends to zero when approaching the magnetic moment compensation temperature.

Abstract—Ferromagnetic resonance (FMR) in planar thin film structures comprised of magnetic cross-shaped elements arranged into square lattices has been studied by micromagnetic simulation. FMR spectra and spatial distributions of amplitudes of resonant oscillations were determined for vortex and antivortex states of magnetization in lattice crosses. Resonant modes have the shape of rotating magnetization distributions. Herewith, modes with the same configuration of magnetization but rotating in reverse directions are frequency split. The observed nonreciprocity of propagation of resonant spin oscillations is determined by the sign of magnetization distribution vorticity.

Abstract—Temperature dependence of attenuation of magnetic spin precession in two-layer structures with a Pt top layer based on a La_0.7Sr_0.3MnO₃ (LSMO) epitaxial manganite film is studied by measuring the width of a ferromagnetic resonance (FMR) line. Ferromagnetic resonance in thin ferromagnetic manganite films is used for the creation of a spin current at the interface between the metallic and ferromagnetic layers. A significant increase in a width of a line in FMR spectrum in two-layer structures due to generation of a spin current, heterogeneity of a ferromagnetic layer, two-magnon scattering, and eddy current is discussed.

Abstract—The optical and magneto-optical properties of the metal–dielectric multilayer [Co/TiO₂]_n structures with 2–4-nm-thick layers prepared on a silicon substrate Si(001) by ion-beam deposition have been studied. The complex permittivity of multilayer [Co/TiO₂]_n structures has been measured by the optical ellipsometry technique in the spectral range of 0.6–5.6 eV and analyzed using the optical reflection matrices for isotropic multilayer dielectric structures taking into account the optical losses and also using the method of anisotropic effective medium. The magneto-optical Kerr effect has been measured by the polarimetric technique in the spectral range of 1.2–4.5 eV in the polar and longitudinal geometries. The magnetic anisotropy type is determined on the base of the field dependences of the magneto-optical Kerr effect. It is found that the nanosized [Co/TiO₂]_n structures can be considered as artificial optically uniaxial media with a strong magnetic and optical anisotropy at room temperature.

Abstract—A procedure for correcting hardness data measured on rough surfaces using instrumented indentation is presented. The correction procedure relies on the knowledge of surface topography, which can be obtained by atomic force microscopy or other appropriate instrumental technique. The analyzed surface is characterized by the standard deviation of height distribution and an autocorrelation function. The latter is proposed to be modeled with an exponential function with either a quadratic or linear exponent.

Abstract—We present the results of synthesis of arrays of gold and bilayer Au/Ni nanorods in a matrix of porous anodic alumina and of experimental investigation and numerical simulation of their optical and magnetooptical properties. We show that the spectra of these structures have two singular features located near 520 nm and in the range of 700–800 nm. Au/Ni nanorods exhibit a significant modulation and enhancement of the magnetooptical intensity effect in the range of the long-wavelength resonance. Experimentally observed features agree with results of numerical simulation.

Abstract—In this paper, we showed the possibility of practical realization of circularly polarized radiation detectors based on a planar photoresistor using the effect of magnetocircular dichroism in the CoPt layer, as well as based on structures using the spin filtration by the CoPt layer of photogenerated spin-polarized charge carriers. The spin filtration process is established to allow increasing the detection efficiency of up to 1.3%.

Abstract—The phonon spectrum of CdGa₂S₄ has been experimentally investigated by Raman spectroscopy and theoretically analyzed using the density functional theory (DFT). Eleven active Raman modes (at 83, 135, 165, 219, 243, 260, 310, 322, 352, 361, and 392 cm^–1) have been detected and identified. The identification of all vibrational modes is based on consideration of the point symmetry group. The results are compared with the existing experimental IR spectroscopy and Raman scattering data.