188 research outputs found
Statistical theory of the excited strip domain structure
A statistical theory of the strip domain structure excited in a bubble film
by an oscillating magnetic field is developed. The theory is based on the
consideration of the strip domain structure as a thermodynamic system
characterized by the spectrum of domain walls oscillation and an effective
temperature that is caused by an oscillating magnetic field and film
nonuniformities. We found the thermodynamic characteristics of that domain
structure and calculated its period as a function of the frequency and
amplitude of an oscillating magnetic field.Comment: 6 pages, 3 figure
Influence of twin structure on flux turbulence near the front of vortex annihilation
The remagnetization of YBCO single crystals is studied by magneto-optical
technique. Different behavior of the annihilation flux front in twinned and
twin-less samples is observed. The specific induction distribution, called
Meissner hole, is found to be necessary forerunner of turbulence development.Comment: 7 pages, 5 figures. to be published in Physica
Dendritic flux avalanches and nonlocal electrodynamics in thin superconducting films
We present numerical and analytical studies of coupled nonlinear Maxwell and
thermal diffusion equations which describe nonisothermal dendritic flux
penetration in superconducting films. We show that spontaneous branching of
propagating flux filaments occurs due to nonlocal magnetic flux diffusion and
positive feedback between flux motion and Joule heat generation. The branching
is triggered by a thermomagnetic edge instability which causes stratification
of the critical state. The resulting distribution of magnetic microavalanches
depends on a spatial distribution of defects. Our results are in good agreement
with experiments performed on Nb films.Comment: 4 pages, 3 figures, see http://mti.msd.anl.gov/aran_h1.htm for
extensive collection of movies of dendritic flux and temperature pattern
Macroturbulent Instability of the Flux Line Lattice in Anisotropic Superconductors
A theory of the macroturbulent instability in the system containing vortices
of opposite directions (vortices and antivortices) in hard superconductors is
proposed. The origin of the instability is connected with the anisotropy of the
current capability in the sample plane. The anisotropy results in the
appearance of tangential discontinuity of the hydrodynamic velocity of vortex
and antivortex motion near the front of magnetization reversal. As is known
from the classical hydrodynamics of viscous fluids, this leads to the
turbulization of flow. The examination is performed on the basis of the
anisotropic power-law current-voltage characteristics. The dispersion equation
for the dependence of the instability increment on the wave number of
perturbation is obtained, solved, and analyzed analytically and numerically. It
is shown that the instability can be observed even at relatively weak
anisotropy.Comment: 10 pages, 5 figures, submitted to Physical Review
Interaction between superconducting vortices and Bloch wall in ferrite garnet film
Interaction between a Bloch wall in a ferrite-garnet film and a vortex in a
superconductor is analyzed in the London approximation. Equilibrium
distribution of vortices formed around the Bloch wall is calculated. The
results agree quantitatively with magneto-optical experiment where an in-plane
magnetized ferrite-garnet film placed on top of NbSe2 superconductor allows
observation of individual vortices. In particular, our model can reproduce a
counter-intuitive attraction observed between vortices and a Bloch wall having
the opposite polarity. It is explained by magnetic charges appearing due to
discontinuity of the in-plane magnetization across the wall.Comment: 4 pages, 5 figure
Triode for Magnetic Flux Quanta
In an electronic triode, the electron current emanating from the cathode is regulated by the electric potential on a grid between the cathode and the anode. Here we demonstrate a triode for single quantum magnetic field carriers, where the flow of individual magnetic vortices in a superconducting film is regulated by the magnetic potential of striae of soft magnetic strips deposited on the film surface. By rotating an applied in-plane field, the magnetic strip potential can be varied due to changes in the magnetic charges at the strip edges, allowing accelerated or retarded motion of magnetic vortices inside the superconductor. Scaling down our design and reducing the gap width between the magnetic stripes will enable controlled manipulation of individual vortices and creation of single flux quantum circuitry for novel high-speed low-power superconducting electronics
Barkhausen noise from zigzag domain walls
We investigate the Barkhausen noise in ferromagnetic thin films with zigzag
domain walls. We use a cellular automaton model that describes the motion of a
zigzag domain wall in an impure ferromagnetic quasi-two dimensional sample with
in-plane uniaxial magnetization at zero temperature, driven by an external
magnetic field. The main ingredients of this model are the dipolar spin-spin
interactions and the anisotropy energy. A power law behavior with a cutoff is
found for the probability distributions of size, duration and correlation
length of the Barkhausen avalanches, and the critical exponents are in
agreement with the available experiments. The link between the size and the
duration of the avalanches is analyzed too, and a power law behavior is found
for the average size of an avalanche as a function of its duration.Comment: 11 pages, 12 figure
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