1,301 research outputs found
Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B != 0 reconnection
International audienceWe investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B != 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B != 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B != 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation
Evolution of magnetic helicity in the course of kinetic magnetic reconnection
International audienceWe investigate the evolution of magnetic helicity density in the course of 2D and 3D kinetic magnetic reconnection through thin current sheets. In 2D, the helicity density near a reconnection X-line becomes purely quadrupolar structured, while in 3D, an additional dipolar structure occurs. This dipolar structure is related to kinetic current instabilities and becomes dominant for spontaneous 3D reconnection, in accordance with the dominating current instabilities. The 2D simulations have been carried out with a newly developed Vlasov-code and the 3D simulations with the particle-in-cell code GISMO
Frustration of the interlayer coupling by mobile holes in La2-xSrxCuO4 (x<0.02)
We have studied the interlayer coupling in the antiferromagnetic (AF) phase
of Sr and Zn doped La2CuO4 by analyzing the spin flip transition in the
magnetization curves. We find that the interlayer coupling strongly depends on
the mobility of the hole charge carriers. Samples with the same hole content as
well as the same Neel temperature but a different hole mobility, which we
adjusted by Zn co-doping, can have a very different interlayer coupling. Our
results suggest that only mobile holes can cause a strong frustration of the
interlayer coupling.Comment: 4 pages, 4 figure
Why of (CaFeAs)PtAs is twice as high as (CaFePtAs)PtAs
Recently discovered (CaFePtAs)PtAs and
(CaFeAs)PtAs superconductors are very similar materials
having the same elemental composition and structurally similar superconducting
FeAs slabs. Yet the maximal critical temperature achieved by changing Pt
concentration is approximately twice higher in the latter. Using angle-resolved
photoemission spectroscopy(ARPES) we compare the electronic structure of their
optimally doped compounds and find drastic differences. Our results highlight
the sensitivity of critical temperature to the details of fermiology and point
to the decisive role of band-edge singularities in the mechanism of high-
superconductivity
Orbital polaron lattice formation in lightly doped La1-xSrxMnO3
By resonant x-ray scattering at the Mn K-edge on La7/8Sr1/8MnO3, we show that
an orbital polaron lattice (OPL) develops at the metal-insulator transition of
this compound. This orbital reordering explains consistently the unexpected
coexistence of ferromagnetic and insulating properties at low temperatures, the
quadrupling of the lattice structure parallel to the MnO2-planes, and the
observed polarization and azimuthal dependencies. The OPL is a clear
manifestation of strong orbital-hole interactions, which play a crucial role
for the colossal magnetoresistance effect and the doped manganites in general
First measurements of the index of refraction of gases for lithium atomic waves
We report here the first measurements of the index of refraction of gases for
lithium waves. Using an atom interferometer, we have measured the real and
imaginary part of the index of refraction for argon, krypton and xenon, as
a function of the gas density for several velocities of the lithium beam. The
linear dependence of with the gas density is well verified. The total
collision cross-section deduced from the imaginary part is in very good
agreement with traditional measurements of this quantity. Finally, as predicted
by theory, the real and imaginary parts of and their ratio
exhibit glory oscillations
Monopolelike probes for quantitative magnetic force microscopy: calibration and application
A local magnetization measurement was performed with a Magnetic Force
Microscope (MFM) to determine magnetization in domains of an exchange coupled
[Co/Pt]/Co/Ru multilayer with predominant perpendicular anisotropy. The
quantitative MFM measurements were conducted with an iron filled carbon
nanotube tip, which is shown to behave like a monopole. As a result we
determined an additional in-plane magnetization component of the multilayer,
which is explained by estimating the effective permeability of the sample
within the \mu*-method.Comment: 3 pages, 3 figure
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