Solid State Phenomena Vol. 190

Abstract: The structural-phase composition, magnetic and microwave properties of Fe_x(SiO₂)_1-x (x=30, 70, 90, 95) nanocomposites have been studied. The composites are produced by high-energy ball milling with either Ar or acetone as a milling medium and milling time of 1 to 64 h. The microwave magnetic properties of the composite in the frequency range of 0.1 to 6 GHz are shown to depend slightly on the phase composition and be governed mainly by the particle size. Reduction of the particle size to about 1 μm results in elimination of magnetic loss at frequencies below 1 GHz, which is attributed to the domain walls motion.

Abstract: The possibility of suppression of gyroscopic magnetization oscillations by increasing an effective in-plane anisotropy field is discussed. It is shown that the presence of biaxial anisotropy in real films with the effective field ranging from 10 to 70 Oe should not cause any difficulties at suppressing the oscillations.

Abstract: Magnetodynamical properties of systems of magnetic nanodisks at the microwave range and low temperatures were studied experimentally. Several periodic square arrays of Permalloy nanodisks deposited onto a glass substrate have been studied. The interdisk center-to-center distance in each array was equal to double disk diameter . The magnetoresonance studies were performed at 70-80 GHz frequency band and at the temperature of 4.2 K. The static external magnetic field was applied perpendicularly to the disks array. As a result the magnetoresonance absorption spectra have been obtained, containing both fundamental mode and spin wave modes. A comparative analysis of the results is performed with the X-band results obtained at T = 300K.

Abstract: Waves in superlattice (SL) contained inhomogeneities with anisotropic correlation properties are considered. The anisotropy of the correlation during the transition from 3D to 2D disorder is characterized by the parameter , where and are the correlation wave numbers along the axis of the SL and in the plane of the its layers, respectively ( and are the correlation radii). Dependencies of both the dynamic susceptibility and density of states at the continuous transition from the isotropic three-dimensional inhomogeneities () to the two-dimensional ones () have been obtained.

Abstract: Analysis of dispersion relations for guided modes in various types of planar three-layer structures containing isotropic layers based of left-handed media (LHM) is carried out. The conditions are studied for the existence of bulk and surface TE and TM modes. The waveguide resonators with distributed feedback are proposed, implemented in a structure with LHM and amplifying guiding layer.

Abstract: Static magnetic properties, ferromagnetic resonance (FMR) and glancing angle X-ray diffraction spectra (GAXRD) of CoFeZr (tm)/Si (tSi) in multilayer nanosystems were investigated for two groups of the samples characterized by t_m = 2 3 nm, t_Si = 0.5 5 nm and by t_m = 7 12 nm, t_Si = 5 13 nm. A computer simulation of GAXRD spectra of multilayer interference structures has been performed taking into account the possibility of silicides formation at metal-Si interfaces. Matter of discussion is the layer and interlayer thickness below which a resonance response corresponds to that of an effective medium rather than of an individual magnetic layer.

Abstract: The role of the geometrical parameters was studied for thin film based [FeNi (100 nm)/Cu (3 nm)]₄/FeNi (100 nm)/Cu (500 nm)/[FeNi (100 nm)/Cu (3 nm)]₄/FeNi (100 nm) magnetoimpedance elements with open magnetic flux prepared by lithography technique. The maximum magnetoimpedance sensitivity of 17 %/Oe was obtained for meander shaped sample, exceeding the value of the maximum sensitivity of 5 %/Oe of the single stripe sample. The highest values of the magnetoimpedance were observed for relatively low frequency of order of 50 MHz convenient for technological applications. Both developed technology and obtained results can be useful for optimization of the design of miniaturized detectors of small magnetic field.

Abstract: High-frequency dynamic magnetic properties of quasi-two-dimensional organic conductors (BEDT-TTF)₂IBr₂ of α'- and β-phases have been studied by Electron Spin Resonance (ESR) spectroscopy. The heating of crystals in the α'-phase is accompanied by their phase transition to the β-phase, so, the Dyson distortion of the ESR line is appeared. Contributions from the crystal field and symmetry of the system as well as the orbital magnetic moment admixture to the total magnetic moment of charge carriers have been judged by the comparison of the orientation and temperature dependencies of the ESR spectra for the α'- and β-phases. Experimental data have proved localized states of charge carriers either in α'- or β-phases.

Abstract: A small angle X-ray scattering experiment was performed on ferrihydrite nanoparticles produced by bacterium Klebsiella oxytoca. Structural investigations of ultrasonicated samples of different concentrations of water-dispersed particles were performed. Model calculations and fitting procedures revealed scattering objects of an elongated shape of 6.73±0.16 nm radius of gyration.

Abstract: In the present study we briefly analyze the cluster structures observed in the model bidisperse ferrofluid constrained in quasi-2D (q2D) layer in the absence of an externally applied magnetic field. We use a combination of a DFT approach and molecular dynamic simulation to quantitatively describe various chain and ring structures and their equilibrium area fractions. We also show that to reach a good agreement between simulation data and theoretical predictions in q2D geometry in theory one needs to allow for more possible chain configurations than in the bulk system. We provide preliminary explanations why the microstructure of bulk bidisperse ferrofluids differs noticeably from the one in q2D layer.