Enhanced superconducting vortex pinning with disordered nanomagnetic arrays

Rosen, Yaniv; Sharoni, Amos; Schuller, Iván K.

doi:10.1103/physrevb.82.014509

Cited by 24 publications

(17 citation statements)

References 35 publications

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“…The deviations shown for f up < 0.8 are related to the presence of a large concentration of repelling centers that induce disorder in the pinning center lattice. Therefore, as observed by Rosen et al, 33 the matching field is reduced compared to its theoretical value.…”

Section: Tunability Of the Matching-field Shiftmentioning

confidence: 84%

Superconducting properties of perforated NbN films using ordered arrays of ferromagnetic nanowires

et al. 2011

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The superconducting properties of NbN thin films deposited perpendicularly and embedding a 100-nm-spaced triangular array of ferromagnetic nanowires have been studied. Matching effects are found to persist up to 3 T in these superconductor-ferromagnet hybrids. Other interesting matching features have been also observed. The first matching field depends on the magnetic history. It can be shifted practically at will between the theoretical matching field H 1 and a lower field H * 1 that depends on the shape of the magnetization hysteretic loop of the nanowires array. Therefore, this shift is strongly influenced by the nanowires packing, in particular by the nanowires diameter in the present system. The reduction of the first matching field is associated with an enhancement of the superconducting state that is the strongest when the first matching field is shifted down to H * 1 . Finally, misleading field-induced superconductivity has been observed in fields up to 1.2 T.

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Section: Tunability Of the Matching-field Shiftmentioning

confidence: 84%

Superconducting properties of perforated NbN films using ordered arrays of ferromagnetic nanowires

et al. 2011

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“…The pinning is enhanced at commensurate fields when the number of vortices equals an integer multiple of the number of pinning sites, but away from these specific matching fields, the enhancement of the critical current is lost 14 . Efforts to enhance the pinning at incommensurate fields have included the use of quasicrystalline substrates 15 or diluted periodic arrays [16][17][18][19][20] , where studies show that new types of non-integer commensurate states can arise in addition to the integer matching configurations. Hyperbolic tessellation arrays were also recently considered 21 .…”

mentioning

confidence: 99%

Strongly Enhanced Pinning of Magnetic Vortices in Type-II Superconductors by Conformal Crystal Arrays

Ray¹,

Jankó²,

Reichhardt³

2013

Phys. Rev. Lett.

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Conformal crystals are non-uniform structures created by a conformal transformation of regular two-dimensional lattices. We show that gradient-driven vortices interacting with a conformal pinning array exhibit substantially stronger pinning effects over a much larger range of field than found for random or periodic pinning arrangements. The pinning enhancement is partially due to matching of the critical flux gradient with the pinning gradient, but the preservation of the sixfold ordering in the conformally transformed hexagonal lattice plays a crucial role. Our results can be generalized to a wide class of gradient-driven interacting particle systems such as colloids on optical trap arrays.PACS numbers: 74.25. Wx,74.25.Uv One of the most important problems for applications of type-II superconductors is how to create high critical currents or strong vortex pinning over a wide range of applied magnetic fields 1 . For over sixty years, it has been understood that the ground state vortex structure is a hexagonal lattice 2 , so many methods have been developed to increase the critical current using uniform pinning arrays that incorporate periodicity to match the vortex structure 3-13 . The pinning is enhanced at commensurate fields when the number of vortices equals an integer multiple of the number of pinning sites, but away from these specific matching fields, the enhancement of the critical current is lost 14 . Efforts to enhance the pinning at incommensurate fields have included the use of quasicrystalline substrates 15 or diluted periodic arrays [16][17][18][19][20] , where studies show that new types of non-integer commensurate states can arise in addition to the integer matching configurations. Hyperbolic tessellation arrays were also recently considered 21 .Part of the problem is the fact that under an applied current, the vortex structure does not remain uniform but instead develops a Bean-like flux gradient 22 : the vortex density is highest at the edges of the sample when the magnetic field is increased, and highest in the center of the sample when the magnetic field is removed and only trapped flux remains inside the sample. As a consequence, uniform pinning arrays generally have a portion of the pinning sites that are not fully occupied, suggesting that a more optimal pinning arrangement should include some type of density gradient to match the critical flux gradient. Here we show that a novel type of pinning structure, created using a conformal transformation of a uniform hexagonal lattice, produces a much higher critical current over a much wider range of magnetic fields than any pinning geometry considered up until now. Conformal crystals not only have a density gradient, but also preserve aspects of the hexagonal ordering naturally adopted by the vortex lattice. The pinning enhancement we find is substantial and will be very important for a wide range of superconductor applications and flux control. Our results can also be important for stabilizing novel self-assembled structures created using de...

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“…12,13 Even, quasiperiodic arrays generate peculiar matching effects 14 and, recently, the interaction between the vortex lattice and short-range ordered arrays of pinning centers has been explored too. 15 Different types of vortices could participate in these phenomena: ͑i͒ vortices placed at the pinning centers that can be single quantized 16 or multiple quantized 17 vortices and ͑ii͒ interstitial vortices placed among pinning centers. 18 In this work, we analyze, vortex lattice matching and ratchet effects, in completely different scenario: symmetric circular dots arranged in a periodic array with broken reflection symmetry so that the origin of the asymmetric pinning potentials is the geometry of the periodic array itself.…”

Section: Introductionmentioning

confidence: 99%

Vortex ratchet reversal at fractional matching fields in kagomélike array with symmetric pinning centers

et al. 2010

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Arrays of Ni nanodots embedded in Nb superconducting films have been fabricated by sputtering and electron-beam lithography techniques. The arrays are periodic triangular lattices of circular Ni dots arranged in a kagomélike pattern with broken reflection symmetry. Relevant behaviors are found in the vortex lattice dynamics: ͑i͒ at values lower than the first integer matching field, several fractional matching fields are present when the vortex lattice moves parallel or perpendicular to the reflection symmetry axis of the array showing a clear anisotropic character in the magnetoresistance curves, ͑ii͒ injecting an ac perpendicular to the reflection symmetry axis of the array yields an unidirectional motion of the vortex lattice ͑ratchet effect͒ as a result of the interaction between the whole vortex lattice and the asymmetric lattice of dots, ͑iii͒ increasing the input current amplitudes the ratchet effect changes polarity independently of matching field values. These experimental results can be explained taking into account the vortex lattice density.

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Enhanced superconducting vortex pinning with disordered nanomagnetic arrays

Cited by 24 publications

References 35 publications

Superconducting properties of perforated NbN films using ordered arrays of ferromagnetic nanowires

Superconducting properties of perforated NbN films using ordered arrays of ferromagnetic nanowires

Strongly Enhanced Pinning of Magnetic Vortices in Type-II Superconductors by Conformal Crystal Arrays

Vortex ratchet reversal at fractional matching fields in kagomélike array with symmetric pinning centers

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