75,501 research outputs found
Testing the Origin of Cosmological Magnetic Fields through the Large-Scale Structure Consistency Relations
We study the symmetries of the post-recombination cosmological
magnetohydrodynamical equations which describe the evolution of dark matter,
baryons and magnetic fields in a self-consistent way. This is done both at the
level of fluid equations and of Vlasov-Poisson-Maxwell equations in phase
space. We discuss some consistency relations for the soft limit of the (n +
1)-correlator functions involving magnetic fields and matter overdensities. In
particular, we stress that any violation of such consistency relations at
equal-time would point towards an inflationary origin of the magnetic field.Comment: 23 page
Barnes Hospital Record
https://digitalcommons.wustl.edu/bjc_barnes_record/1053/thumbnail.jp
The topological description of coronal magnetic fields
Determining the structure and behavior of solar coronal magnetic fields is a central problem in solar physics. At the photosphere, the field is believed to be strongly localized into discrete flux tubes. After providing a rigorous definition of field topology, how the topology of a finite collection of flux tubes may be classified is discussed
Domain - wall - induced magnetoresistance in pseudo spin-valve/superconductor hybrid structures
We have studied the interaction between magnetism and superconductivity in a
pseudo-spin-valve structure consisting of a Co/Cu/Py/Nb layer sequence. We are
able to control the magnetization reversal process and monitor it by means of
the giant magnetoresistance effect during transport measurements. By placing
the superconducting Nb-film on the top of the permalloy (Py) electrode instead
of putting it in between the two ferromagnets, we minimize the influence of
spin scattering or spin accumulation onto the transport properties of Nb.
Magnetotransport data reveal clear evidence that the stray fields of domain
walls (DWs) in the pseudo-spin-valve influence the emerging superconductivity
close to the transition temperature by the occurrence of peak-like features in
the magneto-resistance characteristic. Direct comparison with magnetometry data
shows that the resistance peaks occur exactly at the magnetization reversal
fields of the Co and Py layers, where DWs are generated. For temperatures near
the superconducting transition the amplitude of the DW-induced
magnetoresistance increases with decreasing temperature, reaching values far
beyond the size of the giant magnetoresistive response of our structure in the
normal state.Comment: 20 pages, 4 figure
New Origin For Spin Current And Current-Induced Spin Precession In Magnetic Multilayers
In metallic ferromagnets, an electric current is accompanied by a flux of
angula r momentum, also called spin current. In multilayers, spatial variations
of the spin current correspond to drive torques exerted on a magnetic layer.
These torq ues result in spin precession above a certain current threshold. The
usual kind of spin current is associated with translation of the spin-up and
spin-down Ferm i surfaces in momentum space. We discuss a different kind of
spin current, assoc iated with expansion and contraction of the Fermi surfaces.
It is more nonlocal in nature, and may exist even in locations where the
electrical current density is zero. It is larger than the usual spin current,
in a ratio of 10 or 100, and is dominant in most cases. The new spin current is
proportional to the differenc e Delta-mu = 0.001 eV between spin-up and
spin-down Fermi levels, averaged over the entire Fermi surface. Conduction
processes, spin relaxation, and spin-wave emission in the multilayer can be
described by an equivalent electrical circuit resembling an unbalanced dc
Wheatstone bridge. And Delta-mu corresponds to the output voltage of the
bridge.Comment: 5 pages, 3 figures. To appear in J. Appl. Phys., vol. 89, May 15,
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