368 research outputs found
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Towards a reliable bridge joint between REBCO coated conductors
REBa2Cu3O7-x (REBCO; RE = Y, Gd) coated conductor wires are commercially available up to a length of about 1 km. However, for large-scale devices like superconducting coils for high-field magnets several kilometres of a coated conductors are required. Therefore, it is desirable to use joints, which exhibit similar superconducting properties as the coated conductor itself. In this study, we jointed commercial REBCO coated conductors by a two-step procedure. At first, a superconducting soldering solution was developed and deposited on unstabilized coated conductors via chemical solution deposition. The soldering precursor is based on a Cu-rich solution with a metal cation ratio Y:Ba:Cu of 1:2:4. Secondly, a piece of the coated conductor was delaminated between the superconducting and the buffer layer and used as bridge between two other conductors covered with the soldering layer. Annealing the resulting bridge joint under pressure results in a mechanical stable configuration. © Published under licence by IOP Publishing Ltd
The effect of Ti or Zr additions on the microstructure and magnetic properties of MnAl-C alloys
As-transformed and hot-deformed samples of MnAl-C alloys with Ti or Zr additions have been produced and characterized using magnetometry, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Both Ti and Zr additions in MnAl-C alloys form carbide primary phases, TiC and ZrC, which consume the carbon meant to be dissolved in the metastable τ-phase to stabilize it against decomposition. With these two additions, the Curie temperature of τ-phase increases while its stability against decomposition decreases. After hot deformation, the MnAl-C alloys with Ti or Zr additions have lower polarisation and remanence due to the reduced stability of the τ-phase. Adding extra carbon along with Ti to a MnAl-C alloy in order to compensate for the C lost on formation of TiC restored the original stability of the τ-phase. After hot-deformation, this alloy exhibited a lower polarisation and remanence owing to the unexpected formation of the γ2-phase
Magnetic properties of bi-phase micro- and nanotubes
The magnetic configurations of bi-phase micro- and nanotubes consisting of a
ferromagnetic internal tube, an intermediate non-magnetic spacer, and an
external magnetic shell are investigated as a function of their geometry. Based
on a continuum approach we obtained analytical expressions for the energy which
lead us to obtain phase diagrams giving the relative stability of
characteristic internal magnetic configurations of the bi-phase tubes
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The Influence of Cu-Additions on the Microstructure, Mechanical and Magnetic Properties of MnAl-C Alloys
Alloys of the form (Mn54Al44C2)100-xCux (with x = 0, 1, 2, 4 and 6) were produced by induction melting. After homogenisation and quenching, most of the alloys consist entirely of the retained ε-phase, except for x = 6, in which the κ-phase was additionally present. After subsequent annealing, the alloys with x ≤ 2 consist entirely of a Cu-doped, ferromagnetic τ-phase, whereas the alloys with x > 2 additionally contain the κ-phase. The polarisation of the alloys at an applied field of 14 T decreases with increasing Cu-content, which is attributed i) to the dilution of the magnetic moment of the τ-phase unit cell by the Cu atoms, which do not carry a magnetic moment, and ii) at higher Cu-contents, to the formation of the κ-phase, which has a much lower polarisation than the τ-phase and therefore dilutes the net polarisation of the alloys. The Curie temperature was not affected by the Cu-additions. The stress needed to die-upset the alloys with x ≤ 2 was similar to that of the undoped alloy, whereas it was much lower for x = 4 and 6, due to the presence of intergranular layers of the κ-phase. The extrinsic magnetic properties of alloys with x ≤ 2 were improved by die-upsetting, whereas decomposition of the τ-phase during processing had a deleterious effect on the magnetic properties for higher Cu-additions
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Microstructural defects in hot deformed and as-transformed Ï„-MnAl-C
In this study, detailed microstructural characterisation has been conducted in both as-transformed and hot deformed samples of Ï„-MnAl-C using transmission electron microscopy. After hot deformation, true twins, dislocations, intrinsic stacking faults and precipitates of Mn3AlC are the main defects in the recrystallised grains. True twins and order twins were distinguished based on differences in their diffraction patterns. A significant fraction of non-recrystallised grains existed, which had microstructures based on combinations of high densities of true twins, dislocations, and deformation bands. The formation of the Mn3AlC precipitates was confirmed and related to the reduction of saturation magnetization and the increase in the Curie temperature of Ï„-MnAl-C after hot deformation. Antiphase boundaries, which are believed to act as nucleation sites for reverse domains, were not observed in the hot deformed sample
Domain wall mobility in nanowires: transverse versus vortex walls
The motion of domain walls in ferromagnetic, cylindrical nanowires is
investigated numerically by solving the Landau-Lifshitz-Gilbert equation for a
classical spin model in which energy contributions from exchange, crystalline
anisotropy, dipole-dipole interaction, and a driving magnetic field are
considered. Depending on the diameter, either transverse domain walls or vortex
walls are found. The transverse domain wall is observed for diameters smaller
than the exchange length of the given material. Here, the system behaves
effectively one-dimensional and the domain wall mobility agrees with a result
derived for a one-dimensional wall by Slonczewski. For low damping the domain
wall mobility decreases with decreasing damping constant. With increasing
diameter, a crossover to a vortex wall sets in which enhances the domain wall
mobility drastically. For a vortex wall the domain wall mobility is described
by the Walker-formula, with a domain wall width depending on the diameter of
the wire. The main difference is the dependence on damping: for a vortex wall
the domain wall mobility can be drastically increased for small values of the
damping constant up to a factor of .Comment: 5 pages, 6 figure
Atomic layer deposition of ZnS nanotubes
We report on growth of high-aspect-ratio () zinc sulfide
nanotubes with variable, precisely tunable, wall thicknesses and tube diameters
into highly ordered pores of anodic alumina templates by atomic layer
deposition (ALD) at temperatures as low as 75 C. Various
characterization techniques are employed to gain information on the
composition, morphology, and crystal structure of the synthesized samples.
Besides practical applications, the ALD-grown tubes could be envisaged as model
systems for the study of a certain class of size-dependent quantum and
classical phenomena.Comment: 1 LaTeX source file, 8 eps figures, and the manuscript in PDF forma
Breakdown of Varvenne scaling in (AuNiPdPt) Cu high-entropy alloys
The compositional dependence of the yield strength σ has been studied for a series of polycrystalline (AuNiPdPt)Cu alloys by means of compression tests. σ is found to decrease linearly with increasing Cu concentration. This behaviour is in contradiction to the generalised theory for solid solution strengthening in concentrated solid solutions provided by Varvenne et al. [1]. A breakdown of the scaling behaviour is found as σy should be non-linear and slightly increasing when modifying the composition from AuNiPdPt to AuCuNiPdPt
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