204 research outputs found
Tunable pinning in superconducting films with magnetic micro-loops
We study the flux pinning properties of superconductor/magnetic micro-rings
lattice hybrid structures. The used open triangular micromagnets represent an
eight-fold degree of freedom system, with six polarized and two flux-closure
possible states. By conveniently choosing the magnetic state of the underlying
rings it is possible to induce different pinning potentials. We show that the
magnetic vortex state with minimum stray field produces a weaker pinning in
comparison with the polarized states
Novel pinning phenomena in a superconducting film with a square lattice of artificial pinning centers
We study the transport properties of a superconducting Nb film with a square
lattice of artificial pinning centers (APCs) as a function of dc current, at a
temperature close to the superconducting transition temperature of the film. We
find that, at low dc currents, the differential resistance of the film shows
the standard matching field anomaly, that is, the differential resistance has a
local minimum at magnetic fields corresponding to an integer number of flux
lines per APC. However, at higher dc currents, the differential resistance at
each matching field turns to a local maximum, which is exactly opposite to the
low current behavior. This novel effect might indicate that the flux lines in
the APC system change their flow mode as the dc current is increased.Comment: 10 pages, 4 figure
Magnetic dipole induced guided vortex motion
We present evidence of magnetically controlled guided vortex motion in a
hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of
a square array of permalloy square rings. When the rings are magnetized with an
in-plane external field H, an array of point-like dipoles with moments
antiparallel to H, is formed. The resulting magnetic template generates a
strongly anisotropic pinning potential landscape for vortices in the
superconducting layer. Transport measurements show that this anisotropy is able
to confine the flux motion along the high symmetry axes of the square lattice
of dipoles. This guided vortex motion can be either re-routed by 90 degrees by
simply changing the dipole orientation or even strongly suppressed by inducing
a flux-closure magnetic state with very low stray fields in the rings.Comment: 5 pages, 3 figure
Self organized mode locking effect in superconductor / ferromagnet hybrids
The vortex dynamics in a low temperature superconductor deposited on top of a
rectangular array of micrometer size permalloy triangles is investigated
experimentally. The rectangular unit cell is such that neighboring triangles
physically touch each other along one direction. This design stabilizes
remanent states which differ from the magnetic vortex state typical of
individual non-interacting triangles. Magnetic Force Microscopy images have
revealed that the magnetic landscape of the template can be switched to an
ordered configuration after magnetizing the sample with an in-plane field. The
ordered phase exhibits a broad flux flow regime with relatively low critical
current and a highly anisotropic response. This behavior is caused by the
spontaneous formation of two separated rows of vortices and antivortices along
each line of connected triangles. The existence of a clear flux flow regime
even for zero external field supports this interpretation. The density of
induced vortex-antivortex pairs is directly obtained using a high frequency
measurement technique which allows us to resolve the discrete motion of
vortices. Strikingly, the presence of vortex-antivortex rows gives rise to a
self organized synchronized motion of vortices which manifests itself as field
independent Shapiro steps in the current-voltage characteristics.Comment: 9 pages, 11 figure
Direct observation of superconducting vortex clusters pinned by a periodic array of magnetic dots in ferromagnetic/superconducting hybrid structures
Strong pinning of superconducting flux quanta by a square array of 1
m-sized ferromagnetic dots in a magnetic-vortex state was visualized by
low-temperature magnetic force microscopy (LT-MFM). A direct correlation of the
superconducting flux lines with the positions of the dots was derived. The
force that the MFM tip exerts on the individual vortex in the depinning process
was used to estimate the spatial modulation of the pinning potential. It was
found, that the superconducting vortices which are preferably located on top of
the Py dots experience about 15 times stronger pinning forces as compared to
the pinning force in the pure Nb film. The strong pinning exceeds the repulsive
interaction between the superconducting vortices and allows the vortex clusters
to be located at each dot. Our microscopic studies are consistent with global
magnetoresistace measurements on these hybrid structures.Comment: 4 pages, 4 figure
Temperature dependent dynamic and static magnetic response in magnetic tunnel junctions with Permalloy layers
Ferromagnetic resonance and static magnetic properties of CoFe/Al2O3/CoFe/Py
and CoFe/Al2O3/CoFeB/Py magnetic tunnel junctions and of 25nm thick
single-layer Permalloy(Py) films have been studied as a function of temperature
down to 2K. The temperature dependence of the ferromagnetic resonance excited
in the Py layers in magnetic tunnel junctions shows knee-like enhancement of
the resonance frequency accompanied by an anomaly in the magnetization near
60K. We attribute the anomalous static and dynamic magnetic response at low
temperatures to interface stress induced magnetic reorientation transition at
the Py interface which could be influenced by dipolar soft-hard layer coupling
through the Al2O3 barrier
Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillars
Broadband magnetization response of coupled vortex state magnetic dots in
layered nanopillars was explored as a function of in-plane magnetic field and
interlayer separation. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25
nm) nanopillars of 600 nm diameter, a small in-plane field splits the
eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition
between in-phase and out-of-phase kinds of the low-lying coupled spin wave
modes. The critical field for this splitting is determined by antiparallel
chiralities of the vortices in the layers. Qualitatively similar (although more
gradual) changes occur also in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25
nm) tri-layer nanopillars. These findings are in qualitative agreement with
micromagnetic dynamic simulations
Management of sustainable organizational development of large-scale economic systems
У статі визначено необхідність вдосконалення системи управління організаційно-економічним механізмом забезпечення ефективної організації та стійкого організаційного розвитку підприємства; наведено переваги великомасштабних економічних систем перед іншими організаційними формами; розглянуто поняття "розвиток" та модель життєвого циклу великомасштабних економічних систем.The article defines the necessity of improving the management system of the organizational and economic mechanism for ensuring an effective organization and sustainable organizational development of the enterprise; also there were presented advantages of large-scale economic systems over other organizational forms; the concept of "development" and the life cycle model of large-scale economic systems are considered
- …