Microscopic picture of the critical state in a superconductor with a periodic array of antidots

Silhanek, Alejandro; Gutiérrez, J.; Kramer, R. B. G.; Ataklti, G. W.; Vondel, J. Van de; Moshchalkov, Victor; Sanchez, Alvaro

doi:10.1103/physrevb.83.024509

Cited by 21 publications

(27 citation statements)

References 30 publications

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“…Similar change of slope of B(H) in the initial stages of the flux propagation has been observed before, most recently in case of thin Pb film with periodic pinning array 45 . This feature is usually attributed to demagnetization effects which lead to compression of flux lines close a border of thin film placed in perpendicular magnetic field 55 .…”

Section: Flux Confinement During the Initial Flux Entrysupporting

confidence: 58%

“…Inhomogeneous flux penetration leading to commensurability or channeling effects have been well documented for ordered or quasiordered arrays of pinning centers 5,6 , while in the case of SFB's with stripe domain patterns anisotropic flux entry has been observed 24,44 . Recently, irregular flux penetration in the form of a terraced critical state has been observed by scanning Hall microscopy in thin Pb film with an array of antidots 45 , in agreement with theoretical predictions 46,47 .…”

Section: Introductionsupporting

confidence: 63%

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Tuning vortex confinement by magnetic domains in a superconductor/ferromagnet bilayer

et al. 2013

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We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in between to avoid proximity effect. The magnetic domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature the magnetic pinning increases but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth.

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Section: Flux Confinement During the Initial Flux Entrysupporting

confidence: 58%

Section: Introductionsupporting

confidence: 63%

Tuning vortex confinement by magnetic domains in a superconductor/ferromagnet bilayer

et al. 2013

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“…Attempts for adjusting to more realistic situations included the decrement of critical current with magnetic field, 3 the presence of edge barriers, 4,5 and the existence of a finite lower critical field. 6,7 In most cases, these improvements result in marginal corrections to the simpler Bean approximation.…”

Section: Introductionmentioning

confidence: 99%

Visualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging

et al. 2011

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We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical measurements. The investigated samples are three Nb films: a plain specimen, used as a reference sample, and other two films patterned with square arrays of antidots. At low temperatures and small ac amplitudes of the excitation field, the Meissner screening prevents penetration of flux into the sample. Above a certain ac drive threshold, flux avalanches are triggered during the first cycle of the ac excitation. The subsequent periodic removal, inversion, and rise of flux occurs essentially through the already-created dendrites, giving rise to an ac susceptibility signal weakly dependent on the applied field. The intradendrite flux oscillation is followed, at higher values of the excitation field, by a more drastic process consisting of creation of new dendrites and antidendrites. In this more invasive regime, the ac susceptibility shows a clear field dependence. At higher temperatures a smooth penetration occurs, and the flux profile is characteristic of a critical state. We have also shown that the regime dominated by vortex avalanches can be reliably identified by ac susceptibility measurements.

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“…For example, for random pinning arrays it has been found that certain regions where the pinning density is slightly lower lead to the formation of persistent river-like flow patterns 32 ; these structures are unable to form in the CPA. For periodic pinning arrangements, easy vortex flow occurs along the symmetry directions of the pinning array 33,34 , causing a drop in the critical current above a commensurate field. Such motion is suppressed in the CPA due to the arching structure.…”

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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Microscopic picture of the critical state in a superconductor with a periodic array of antidots

Cited by 21 publications

References 30 publications

Tuning vortex confinement by magnetic domains in a superconductor/ferromagnet bilayer

Tuning vortex confinement by magnetic domains in a superconductor/ferromagnet bilayer

Visualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging

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

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