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Giant magnetoimpedance (GMI) [FeNi/Cu]4/FeNi/Cu/[FeNi/Cu]4/FeNi sensing meander elements were designed and tested aiming to develop a new instrumentation for characterization of polymer/magnetic nanoparticles composites. Acrylic copolymer of 95% of butyl methacrylate and 5% of methacrylic acid was used as polymer matrix of the composite. It was shown that GMI meander sensing elements are capable of detecting Ni nanoparticles spread in the polymer matrix. Polymeric composites filled with magnetic nanoparticles in small concentration are able to enhance GMI meander sensitivity. [ABSTRACT FROM AUTHOR]

Magnetic properties and the magnetoimpedance (MI) effect were studied for a series of [Fe20Ni80 /Ti]n /Fe20Ni80(n=0 to 5) nanostructures, prepared by dc magnetron sputtering. The thickness of the FeNi layers was selected as 170 nm in order to avoid the appearance of the "transcritical" state that takes place for thicker layers. First, the influence of the Ti layer thickness was determined for n=1 trilayers, with Ti layers ranging from 2 to 20 nm. The minimum coercivity corresponded to a Ti layer of about 6 nm. Second, the magnetic properties and MI responses were studied for different [Fe20Ni80 /Ti]n /FeNi structures at a fixed Ti layer thickness of 6 nm. The complex impedance was measured for a frequency range of 1-300 MHz. The highest value of the MI was obtained in the sample [FeNi/Ti]5/FeNi with the largest total thickness. [ABSTRACT FROM AUTHOR]

Two-dimensional hybrid numerical simulations of E×B discharges used in Hall thruster propulsion point to the presence of strong fluctuations attributable to resistive instabilities in the frequency range of f≈0.1–10 MHz and the wavenumber range of λ-1≈10–500 m-1. Analytical analyses confirm that these resistive modes are of the convective type, become increasingly unstable at low electron mobility, and are particularly intense at high voltage. The simulations, which model cross-field electron flow via an experimentally measured mobility, exhibit large fluctuation power in a region corresponding to a strong electron transport barrier. The analysis gives an electron mobility (μe) -dependent growth rate (γ) scaling as γ∼μe-1/2. The predicted phase velocity of these waves is close to the ion velocity, somewhat lower than that seen in the simulations. Including the electron pressure contribution lowers the growth rate at high frequencies, and introduces a phase velocity that is shifted by ± the ion acoustic speed for the stable and unstable branch, respectively. Surprisingly, the phase velocity of the strong disturbances at high frequency seen in the simulations is found to be in agreement with that of the initially stable branch. Finite ionization/particle wall recombination does not change the overall conclusions at high frequencies. However, at lower f or larger λ, the growth rate of the instability is dominated by the ionization rate, and the disturbances are better described as “ionization” instabilities. The transition/competition between ionization, electron pressure, and resistive behavior gives rise to a “quiescent frequency band” where the growth rate is found to be small, consistent with what is seen in the numerical experiments. While simple linear analysis captures much of the observed simulation behavior, comparison with limited experimental data at low frequency suggests that other effects, in particular azimuthal dynamics, are very important, and further motivate extending the hybrid simulation models to three dimensions. [ABSTRACT FROM AUTHOR]

Studies a drift-Alfven magnetoturbulence model that augments reduced magnetohydrodynamics with evolution of electron density under parallel compression and fluid advection. Spectral transfer rates; Frequency spectra; Energy partitions; Ensemble-averaged turbulent response; RMS turbulent frequency.

Examines the compressible electron magnetoturbulence two-dimensional paradigm for magnetic turbulence coupled to electron density fluctuations. Partitions of magnetic and internal energies in steady states; Effect on the turbulent response by diamagnetic rotation and short-wavelength fluctuations of density.

Derives a procedure for calculating the nonlinear energy transfer and linear growth/damping rate of fully developed turbulence. Enforcement of the stationarity of the turbulence to reduce the effects of noise and fluctuations not described by the basic governing equation; Reconstruction of the input growth rate and nonlinear coupling coefficients.

The microstructure and magnetic properties of sputtered permalloy films and FeNi(170 nm)/X/FeNi(170 nm) (X = Co, Fe, Gd, Gd-Co) sandwiches were studied. Laminating of the thick FeNi film with various spacers was done in order to control the magnetic softness of FeNi-based multilayers. In contrast to the Co and Fe spacers, Gd and Gd-Co magnetic spacers improved the softness of the FeNi/X/FeNi sandwiches. The magnetoimpedance responses were measured for [FeNi/Ti(6 nm)]2/FeNi and [FeNi/Gd(2 nm)]2/FeNi multilayers in a frequency range of 1-500 MHz: for all frequencies under consideration the highest magnetoimpedance variation was observed for [FeNi/Gd(2 nm)]2/FeNi multilayers. [ABSTRACT FROM AUTHOR]