177 research outputs found
Studies of Charge Exchange in a HighâPressure Pulsed Electron Impact Source
This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/56/3/10.1063/1.1677327.A high pressure pulsed ion source has been used in a timeâofâflight mass spectrometer in order to study the charge exchangereactions in ArâH2 and ArâD2 systems using the ion source in the ÄermĂĄk mode of operation. As the source was used in a pulsed mode, it was possible to identify the various secondary ions arising from the charge exchangereactions in these systems. Very good agreement has been shown to exist between the experimental results and simple theoretical deductions. Calculations have been made to determine the cross sections for the charge exchangereactions between the various species from the experimental data
Thin static charged dust Majumdar-Papapetrou shells with high symmetry in D >= 4
We present a systematical study of static D >= 4 space-times of high symmetry
with the matter source being a thin charged dust hypersurface shell. The shell
manifold is assumed to have the following structure S_(beta) X R^(D-2-beta),
beta (in the interval ) is dimension of a sphere S_(beta). In case
of (beta) = 0, we assume that there are two parallel hyper-plane shells instead
of only one. The space-time has Majumdar-Papapetrou form and it inherits the
symmetries of the shell manifold - it is invariant under both rotations of the
S_(beta) and translations along R^(D-2-beta). We find a general solution to the
Einstein-Maxwell equations with a given shell. Then, we examine some flat
interior solutions with special attention paid to D = 4. A connection to D = 4
non-relativistic theory is pointed out. We also comment on a straightforward
generalisation to the case of Kastor-Traschen space-time, i.e. adding a
non-negative cosmological constant to the charged dust matter source.Comment: Accepted in Int. J. Theor. Phy
Magnonic Weyl states in Cu2OSeO3
The multiferroic ferrimagnet CuOSeO with a chiral crystal structure
attracted a lot of recent attention due to the emergence of magnetic skyrmion
order in this material. Here, the topological properties of its magnon
excitations are systematically investigated by linear spin-wave theory and
inelastic neutron scattering. When considering Heisenberg exchange interactions
only, two degenerate Weyl magnon nodes with topological charges 2 are
observed at high-symmetry points. Each Weyl point splits into two as the
symmetry of the system is further reduced by including into consideration the
nearest-neighbor Dzyaloshinsky-Moriya interaction, crucial for obtaining an
accurate fit to the experimental spin-wave spectrum. The predicted topological
properties are verified by surface state and Chern number analysis.
Additionally, we predict that a measurable thermal Hall conductivity can be
associated with the emergence of the Weyl points, the position of which can be
tuned by changing the crystal symmetry of the material
Pressure-induced huge increase of Curie temperature of the van der Waals ferromagnet VI3
Evolution of magnetism in single crystals of the van der Waals compound VI3
in external pressure up to 7.3 GPa studied by measuring magnetization and ac
magnetic susceptibility is reported. Four magnetic phase transitions, at T1 =
54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed
at ambient pressure. The first two have been attributed to the onset of
ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is
characterized by the magnetic ordering transition at Curie temperature TC and
the transition between two different ferromagnetic phases TFM, accompanied by a
structure transition from monoclinic to triclinic symmetry upon cooling. The
pressure effects on magnetic parameters were studied with three independent
techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa
whereas TFM increases rapidly with increasing pressure and reaches TC at a
triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase
transition is observed moving to higher temperatures with increasing pressure
to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization
is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa)
suggesting a possible pressure-induced reduction of vanadium magnetic moment.
We discussed these results in light of recent theoretical studies to analyze
exchange interactions and provide how to increase the Curie temperature of VI3.Comment: 20 pages, 16 figure
Guided assembly of nanoparticles on electrostatically charged nanocrystalline diamond thin films
We apply atomic force microscope for local electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon, to induce electrostatically driven self-assembly of colloidal alumina nanoparticles into micro-patterns. Considering possible capacitive, sp2 phase and spatial uniformity factors to charging, we employ films with sub-100 nm thickness and about 60% relative sp2 phase content, probe the spatial material uniformity by Raman and electron microscopy, and repeat experiments at various positions. We demonstrate that electrostatic potential contrast on the NCD films varies between 0.1 and 1.2 V and that the contrast of more than Âą1 V (as detected by Kelvin force microscopy) is able to induce self-assembly of the nanoparticles via coulombic and polarization forces. This opens prospects for applications of diamond and its unique set of properties in self-assembly of nano-devices and nano-systems
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