Search results for "06"
showing 10 items of 26305 documents
Study of the multipactor phenomenon using a full-wave integral equation technique
2017
Abstract Multipactor effect is a well-known phenomenon of RF breakdown in satellite payloads which degrades components, generates undesirable harmonics, contributes to power dissipation and increases noise in communications. Traditionally, multipactor has been investigated with the aim of obtaining the so-called multipactor threshold voltage, or to present different multipaction detection methods. However, very little attention has been focused on analysing this phenomenon using a multimodal approach. The main goal of this work is to analyse the interaction between a multipactor current and a realistic microwave cavity by means of a rigorous and accurate formulation. For the first time to t…
Conceptual study of a heavy-ion-ERDA spectrometer for energies below 6 MeV
2017
Abstract Elastic recoil detection analysis (ERDA) is a well established technique and it offers unique capabilities in thin film analysis. Simultaneous detection and depth profiling of all elements, including hydrogen, is possible only with time-of-flight ERDA. Bragg ionization chambers or Δ E - E detectors can also be used to identify the recoiling element if sufficiently high energies are used. The chief limitations of time-of-flight ERDA are the beam induced sample damage and the requirement of a relatively large accelerator. In this paper we propose a detector setup, which could be used with 3 MeV to 6 MeV medium heavy beams from either a single ended accelerator (40Ar) or from a tandem…
Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/nonmagnetic metal/ferromagnet multilayered stacks
2017
In this work we focus on magnetic relaxation in Mn80Ir20(12 nm)/Cu(6 nm)/Py(dF) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM) multilayers with different thickness of the ferromagnetic permalloy layer. An effective FM-AFM interaction mediated via the conduction electrons in the nonmagnetic Cu spacer – the spin-pumping effect – is detected as an increase in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of the resonant magnetic field. We further find experimentally that the spin-pumping-induced contribution to the linewidth is inversely proportional to the thickness of the Py layer. We show that this thickness dependence likely originates from the dissipative dynamics of …
Numerical values of MnZn ferrite nonlinear susceptibilities in a lossless approximation
2017
On the basis of expressions for nonlinear magnetic susceptibilities of soft ferrites obtained earlier the analysis of phase shifts between components of flux density on different frequencies and the magnetic field strength is carried out. Only the largest nonlinear susceptibilities those of third and fifth order are considered. It is shown that in the frequency range where losses are small and can be neglected the susceptibility of third order is negative but that of fifth order is positive. These statements allow explaining the shape of output voltage of toroidal transformer with soft ferrite core induced by strong harmonic field strength in the input. Numerical values of nonlinear suscept…
Double resonance response in nonlinear magnetic vortex dynamics
2013
We present experimental evidences for the dynamical bifurcation behavior of ac-driven magnetic vortex core gyration in a ferromagnetic disk. The dynamical bifurcation, i.e., appearance and disappearance of two stable dynamical states in the vortex gyration, occurring as the amplitude of the driving Oersted field increases to ${B}_{Oe}g{B}_{Oe}^{cr}$, manifests itself in a double resonance response in the dependence of homodyne the dc-voltage signal on the frequency $\ensuremath{\omega}$ of the applied microwave current. We find that the frequency range $\ensuremath{\delta}\ensuremath{\omega}$ between the two resonance features strongly increases with the excitation power. Our analysis based…
Unusual domain-wall motion in ferromagnetic semiconductor films with tetragonal anisotropy
2009
International audience; Magnetic field-driven domain-wall propagation in the flow regime is investigated in (Ga, Mn) As ferromagnetic semiconductor layers. Square-shape magnetic domains with an unexpected orientation of their edges, at pi/8 with respect to the anisotropy axes, are found. This is shown to arise from the effect of tetragonal magnetic anisotropy on domain-wall dynamics. Using a one-dimensional model for domain-wall motion and modeling domain growth by contour dynamics the shape and orientation of domains and their field range for existence are well reproduced. These results point to the key role of the vectorial nature of the order parameter in the dynamics of ferromagnetic do…
Electromagnetically induced switching of ferroelectric thin films
2007
We analyze the interaction of an electromagnetic spike (one cycle) with a thin layer of ferroelectric medium with two equilibrium states. The model is the set of Maxwell equations coupled to the undamped Landau-Khalatnikov equation, where we do not assume slowly varying envelopes. From linear-scattering theory, we show that low-amplitude pulses can be completely reflected by the medium. Large-amplitude pulses can switch the ferroelectric. Using numerical simulations and analysis, we study this switching for long and short pulses, estimate the switching times, and provide useful information for experiments.
Switching by Domain-Wall Automotion in Asymmetric Ferromagnetic Rings
2017
A ring-shaped magnetic logic device offers two vortex states (clockwise and counterclockwise) to encode bits, with relative stability against external magnetic fields. The dynamics of magnetization switching in such structures, though, still need unraveling. The authors present direct experimental visualization of reproducible, robust switching in magnetic rings via domain-wall automotion, which does not require an applied field. Simulations reveal that annihilation of domain walls through automotion always occurs, with the detailed topology of the walls only influencing the dynamics locally, in line with the experimental results.
Transport properties of Bi2Sr2Ca2Cu3O10+δ Bicrystal Grain Boundary Josephson Junctions and SQUIDs
1996
Josephson junctions and SQUIDs on 36.8° SrTiO 3 bicrystal substrates were prepared from epitaxial Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ thin films with critical temperatures around 95K. The current-voltage characteristics are well described by the resistively and capacitively shunted junction model. I c R n products of 50μV at 77K and 0.7mV at 4.2K have been reached. The I c (B) dependence is symmetric to B = 0 with an I c suppression of 90% in the first minimum. Nevertheless it turns out, that the junctions are inhomogeneous on a μm scale. SQUID modulations observed at 78K indicate a flux-voltage transfer function of 2.7μV/Φ 0 at this temperature.
Commissioning of the vacuum system of the KATRIN Main Spectrometer
2016
The KATRIN experiment will probe the neutrino mass by measuring the β-electron energy spectrum near the endpoint of tritium β-decay. An integral energy analysis will be performed by an electro-static spectrometer (``Main Spectrometer''), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m[superscript 3], and a complex inner electrode system with about 120 000 individual parts. The strong magnetic field that guides the β-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. A system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter strips ha…