8,492 research outputs found
Parametric frequency mixing in the magneto-elastically driven FMR-oscillator
We demonstrate the nonlinear frequency conversion of ferromagnetic resonance
(FMR) frequency by optically excited elastic waves in a thin metallic film on
dielectric substrates. Time-resolved probing of the magnetization directly
witnesses magneto-elastically driven second harmonic generation, sum- and
difference frequency mixing from two distinct frequencies, as well as
parametric downconversion of each individual drive frequency. Starting from the
Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an
elastically driven nonlinear parametric oscillator and show that frequency
mixing is dominated by the parametric modulation of FMR frequency
Regional Investment Policy Under the Impact of Budget Limitations and Economic Sanctions
The article is devoted to the assessment of influence of budgetary restrictions and economic sanctions on investment policy of a region. The paper studies the bilateral negative effect on socio-economic development of regions from both the external sanctions and braking mechanism of economic development within the country. On the basis of the comparative and statistical analysis, the need to change focus of investment policy from the growth in volumes to qualitative perfecting is proved. The new direction of investment policy connected with the import substitution process realization, its combination with acceleration of innovative development on the certain example of Sverdlovsk region is analyzed. The conclusions and offers stated in the article are applicable to the public authorities of subjects of the Russian Federation, experts in the sphere of regional investment policy and improvement of investment climate, and also the specialized organizations specialized in attracting investment and work with investors in regions of Russia
Dendritic flux penetration in Pb films with a periodic array of antidots
We explore the flux-jump regime in type-II Pb thin films with a periodic
array of antidots by means of magneto-optical measurements. A direct
visualization of the magnetic flux distribution allows to identify a rich
morphology of flux penetration patterns. We determine the phase boundary
between dendritic penetration at low temperatures and a smooth flux
invasion at high temperatures and fields. For the whole range of fields and
temperatures studied, guided vortex motion along the principal axes of the
square pinning array is clearly observed. In particular, the branching process
of the dendrite expansion is fully governed by the underlying pinning topology.
A comparative study between macroscopic techniques and direct local
visualization shed light onto the puzzling and independent magnetic
response observed at low temperatures and fields. Finally, we find that the
distribution of avalanche sizes at low temperatures can be described by a power
law with exponent
Shock waves in superconducting cosmic strings: growth of current
Intrinsic equations of motion of superconducting cosmic string may admit
solutions in the shock-wave form that implies discontinuity of the current term
\chi. The hypersurface of discontinuity propagates at finite velocity
determined by finite increment \Delta \chi =\chi_+ -\chi_-. The current
increases \chi_+>\chi_- in stable shocks but transition between spacelike (\chi
>0) and timelike (\chi<0) currents is impossible.Comment: 13 pages, 3 figure
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
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
Hydrodynamic Instability of the Flux-antiflux Interface in Type-II Superconductors
The macroturbulence instability observed in fluxline systems during
remagnetization of superconductors is explained. It is shown that when a region
with flux is invaded by antiflux the interface can become unstable if there is
a relative tangential flux motion. This condition occurs at the interface when
the viscosity is anisotropic, e.g., due to flux guiding by twin boundaries in
crystals. The phenomenon is similar to the instability of the tangential
discontinuity in classical hydrodynamics. The obtained results are supported by
magneto-optical observations of flux distribution on the surface of a YBCO
single crystal with twins.Comment: 12 pages, 3 figures, submitted to Physical Review Letter
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