Entry of magnetic flux into a magnetically shielded type-II superconductor filament

Applied Physics Letters

Genenko

2014

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Cloaking of static magnetic fields by a finite thickness type-II superconductor tube surrounded by a coaxial paramagnet shell is studied. On the basis of exact solutions to the London and Maxwell equations, it is shown that perfect cloaking is realizable for arbitrary geometrical parameters including the thin film case for both constituents. In contrast to the previous approximate studies assuming perfect diamagnetism of the superconductor constituent, it is proven that cloaking provides simultaneously full undetectability, that is the magnetic moment of the structure completely vanishes as well as all high-order multipole moments as soon as the uniform field outside remains unaffected.

Section: Appendix C: Magnetic Moment Of a Single Vortex Loop At Cloakmentioning

confidence: 99%

Magnetic detectability of a finite size paramagnet/superconductor cylindrical cloak

Applied Physics Letters

Genenko

2014

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“…This means that the presence of the SM constituent reduces the critical dipole moment, and hence facilitates vortex penetration into the SC constituent. By contrast, when the MD faces the SM constituent, m c1 rises monotonically with increasing thickness or relative permeability of the SM constituent, tending to a linear increase for large values of the latter quantity; behaviour resembling that of a magnetically shielded cylindrical SC filament 8,9 . Hence, for this location of the MD, the SM layer can significantly inhibit vortex penetration into the SC constituent, preserving the latter in the Meissner state.…”

mentioning

confidence: 99%

“…This is especially true of heterostructures involving planar superconductors (SCs) and ferromagnetic dots (FDs) which bring about an enhancement of vortex pinning and, concomitantly, an increase of the SC critical current and critical field 1,2,3 . Soft-magnet (SM) constituents offer the possibility to greatly improve the performance of SCs by shielding the transport current self-induced magnetic field as well as an externally imposed magnetic field 4, 5,6,7,8,9 . Here, we study the penetration of the magnetic field of a magnetic dipole (MD) of zero extent (deemed to represent a small FD) into a bilayered SC/SM heterostructure, when the MD faces the SC or the SM constituent.…”

mentioning

confidence: 99%

Magnetic-dipole induced appearance of vortices in a bilayered superconductor/soft-magnet heterostructure

Physica C: Superconductivity

Yampolskaya

Rauh

2007

The penetration of the magnetic field of an infinitesimal magnetic dipole into a bilayered type-II superconductor/soft-magnet heterostructure is studied on the basis of the classical London approach.The critical values of the dipole moment for the first appearance of a single magnetic vortex and, respectively, a magnetic vortex-antivortex pair in the superconductor constituent are obtained, when the magnetic dipole faces the superconductor or the soft-magnet constituent. This reveals that the soft-magnet constituent inhibits penetration of vortices into the superconductor constituent, when the dipole faces the soft-magnet constituent.PACS numbers: 74.25. Op, 74.78.Fk Heterostructures built from superconducting and magnetic materials have attracted much attention during the past few years. This is especially true of heterostructures involving planar superconductors (SCs) and ferromagnetic dots (FDs) which bring about an enhancement of vortex pinning and, concomitantly, an increase of the SC critical current and critical field 1,2,3 . Soft-magnet (SM) constituents offer the possibility to greatly improve the performance of SCs by shielding the transport current self-induced magnetic field as well as an externally imposed magnetic field 4,5,6,7,8,9 . Here, we study the penetration of the magnetic field of a magnetic dipole (MD) of zero extent (deemed to represent a small FD) into a bilayered SC/SM heterostructure, when the MD faces the SC or the SM constituent. Making recourse to the classical London approach, we compare the conditions for the first appearance of a single magnetic vortex and, respectively, a magnetic vortex-antivortex pair in the SC constituent.Let us consider an infinitely extended heterostructure made up of a type-II SC layer with thickness d S and a SM layer with thickness d M , and a nearby MD, its moment m being directed towards the heterostructure. The relative permeability, µ, is assumed as the only material characteristic of the SM constituent, apart from the permeability of free space, µ 0 . The condition for the first vortex appearance follows from the Gibbs free energy of the SC/SM heterostructure due to the presence of a single vortex, G v , which is the sum of the vortex self-energy and the MD-vortex interaction energy. Minimization of G v with respect to the MD-vortex spacing projected onto the SC/SM interface of the heterostructure and imposition of the requirement G v = 0 yields the critical dipole moment m c1 provoking the first vortex appearance in the SC constituent.As has been established before, m c1 falls monotonically with increasing thickness or relative permeability of the SM constituent, when the MD faces the SC constituent 10 . This means that the presence of the SM constituent reduces the critical dipole moment, and hence facilitates vortex penetration into the SC constituent. By contrast, when the MD faces the SM constituent, m c1 rises monotonically with increasing thickness or relative permeability of the SM constituent, tending to a linear increase for large value...

“…Implying an insulating, nonmagnetic layer of thickness much less than d M and d S between the superconductor and the magnet sheath, which is typical for hybrid magnet/superconductor structures (see, for example, Refs. 29,30 ), the boundary conditions read 20 31,32 ), with µ 0 permeability of vacuum. In addition, the magnetic field outside the structure has to approach asymptotically the applied field H 0 .…”

mentioning

confidence: 99%

Magnetic cloaking by a paramagnet/superconductor cylindrical tube in the critical state

Applied Physics Letters

Genenko

2014

Self Cite

Cloaking of static magnetic fields by a finite thickness type-II superconductor tube being in the full critical state and surrounded by a coaxial paramagnet shell is studied. On the basis of exact solutions to the Maxwell equations, it is shown that, additionally to previous studies assuming the Meissner state of the superconductor constituent, perfect cloaking is still realizable at fields higher than the field of full flux penetration into the superconductor and for arbitrary geometrical parameters of both constituents. It is also proven that simultaneously the structure is fully undetectable under the cloaking conditions. Differently from the case of the Meissner state the cloaking properties in the application relevant critical state are realized, however, only at a certain field magnitude.A great research activity has been focused last time on electromagnetic metamaterials which exhibit many unique features, providing particularly cloaking of electromagnetic waves as well as of low frequency and static magnetic or electric fields [1][2][3][4][5][6][7][8] . A magnetic cloak is expected to retain undistorted the external field outside the cloak, thus being "invisible" for external observation, and, as far as possible, to protect its inner area from the external field penetration. To fulfill these requirements, different cloak designs have been proposed, including hybrid systems consisting of ferromagnet and superconductor constituents 8-13 which were recently experimentally realized in the forms of multilayered 14 or bilayered 15,16 magnet/superconductor hollow cylinder. An essential component of the proposed hybrid cylindrical designs is the inner superconducting layer which was assumed until quite recently to be an ideal diamagnetic medium with zero effective permeability in both analytical and finite-element considerations 10,15 . This assumption is, however, unrealistic because of (1) finite field penetration depth which can be comparable with superconductor thickness and (2) massive magnetic flux penetration followed by formation of the critical state typical of magnetic shielding applications [17][18][19] . The system with the finite penetration depth of magnetic field into a superconductor never completely protects the inner region (a central hole) from the penetration of weak external field even in the Meissner state 20 . On the other hand, a non-distorted uniform magnetic field outside the cloak can exist in a wide range of relative permeability and thickness values of the paramagnet sheath for both cases of thick and thin superconductor layers being in the Meissner state. At the same time, the magnetic moment of such a bilayer tube vanishes under the cloaking conditions (as well as all higher multipole moments) making this object magnetically undetectable. Moreover, penetration of magnetic flux into a superconductor in the form of single vortices produces rather small a) Electronic address: yampolsk@mm.tu-darmstadt.de paramagnetic moment of the system, thus breaking the perfect cloaking only slightl...