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Current flow and flux pinning properties of YBCO foam struts

Current flow and flux pinning properties of YBCO foam struts

As mentioned before, the foam samples may be applied as trapped field (TF) magnets, where the improved oxygenation and the reduced weight may enable their use even in space applications. To properly design such systems, modelling of the real foam structure is an important issue, considering both superconducting and mechanical parameters. Therefore, we investigate here in detail the flux pinning properties of in total seven individual foam struts, broken off from one side of the original big foam sample. The study of single foam struts ensures that the current flow is not influenced by percolation effects around the pores. For analysis of the magnetization data, we apply the pinning force scaling approach of Dew- Hughes (DH) [13] to determine the peak positions, h 0 , and
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Flux pinning in PrFeAsO0.9 and NdFeAsO0.9F0.1 superconducting crystals

Flux pinning in PrFeAsO0.9 and NdFeAsO0.9F0.1 superconducting crystals

such as the resistance or irreversible magnetization, may be complicated by material inhomogeneity on mesoscopic or macroscopic length scales. On the other hand, mi- croscopic disorder is well-known to be beneficial for vor- tex line pinning and high critical currents. Finally, from the defect-vortex interaction, one might hope to extract information on electronic scattering mechanisms in the iron-pnictide superconductors, as well as on the premise of phase co-existence. In underdoped pnictides especially, it has been argued that the coexistence of the low-doping anti-ferromagnetic state and the superconducting state at higher doping levels may affect physical properties. 9
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Disorder and flux pinning in superconducting pnictide single crystals

Disorder and flux pinning in superconducting pnictide single crystals

Cornelis Jacominus van der Beek, Giancarlo Rizza, Marcin Konczykowski, Pierre Fertey, Isabelle Monnet, Ryuji Okazaki, Terukazu Kato, Kenishiro. Hashimoto, M[r]

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Pinning force scaling of electrospun Bi-2212 nanowire networks

Pinning force scaling of electrospun Bi-2212 nanowire networks

and the subsequent heat treatment have an extremely low den- sity and show numerous interconnects between the nanowires which enable a current flow through the entire network. The transport and magnetization measurements [2, 4] revealed that the currents can flow through the entire sample perimeter even at applied magnetic fields of 10 T. These properties of the nanowire network samples are very interesting from the under- lying physics and for possible applications. Therefore, in this letter, we analyze the flux pinning forces obtained from M(H) measurements using the model of Dew-Hughes (DH) [5, 6] to gain a deeper understanding of the magnetic behavior of the nanowire networks, which may be interesting for certain ap- plications whereever the weight of the samples counts, and we compare the resulting pinning force scaling diagrams to such of other types of Bi-2212 and Bi-2223 materials published in the
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On the origin of the sharp, low-field pinning force peaks in MgB2 superconductors

On the origin of the sharp, low-field pinning force peaks in MgB2 superconductors

Due to the second point, the currents and flux pinning forces are affected by the given anisotropy of the material. 41 Following the cal- culations of Eisterer, 42 the position of the GB pinning peak may be obtained in the range between 0.1 and 0.2, which is, indeed, the case for the sharp, low-field peaks observed here. In this range, the dominating flux pinning is provided by the GBs, and the current flow is affected by the crystal anisotropy and percolation. When a field-induced decoupling occurs, the currents will only cycle in small regions with the minimum size of an individual grain. Then, anisotropy and percolation do not play the important role any- more, and we will have a situation corresponding to polycrystalline YBa 2 Cu 3 O x . As there is no texture of the MgB 2 grains, the differ-
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Strong pinning and vortex energy distributions in single-crystalline Ba(Fe1−xCox)2As2

Strong pinning and vortex energy distributions in single-crystalline Ba(Fe1−xCox)2As2

(Dated: September 21, 2011) The interrelation between heterogeneity and flux pinning is studied in Ba(Fe 1 − x Co x ) 2 As 2 single crystals with widely varying Co-content x. Magnetic Bitter decoration of the superconducting vortex ensemble in crystals with x = 0.075 and x = 0.1 reveal highly disordered vortex structures. The width of the Meissner belt observed at the edges of the crystals, and above the surface steps formed by cleaving, as well as the width of the intervortex distance distribution, indicate that the observed vortex ensemble is established at a temperature just below the critical temperature T c . The vortex
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Vortex pinning : a probe for nanoscale disorder in iron-based superconductors

Vortex pinning : a probe for nanoscale disorder in iron-based superconductors

Fig. 4 shows the vortex ensemble in single crystalline Ba(Fe 0 .9 Co 0 .1 ) 2 As 2 (with T c = 19.5 K), at H a = 10 G (1 mT). Vortex positions are revealed using Bitter decoration at 4.2 K, after field-cooling through the superconducting transition [8]. The featureless Fourier transform of the set of vortex positions indicates the absence of long–range positional- or orientational order, and the presence of large fluctuations in the nearest-neighbor distance. The very dis- ordered vortex structure is the combined result of the narrow temperature trajectory over which it is frozen in during field-cooling and the importance of flux pinning at high T [8].
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Lower Bounds for Pinning Lines by Balls

Lower Bounds for Pinning Lines by Balls

if there is an ordering on F such that every h d members have a line transversal consistent with that ordering. The smallest such constant h d is at most 2d and at least the size of the largest minimal pinning family of disjoint balls in R d ; Theorem 2 implies that this number is 2d − 1 or 2d. Similarly, we obtain that 2d − 1 is a lower bound for the Helly number of the generalization of Helly’s theorem to sets of transversals to disjoint (unit) balls.

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Domain wall pinning in a circular cross-section wire with modulated diameter

Domain wall pinning in a circular cross-section wire with modulated diameter

Abstract Domain wall propagation in cylindrical nanowires with modulations of diam- eter is a key phenomenon to design physics-oriented devices, or a disruptive three-dimensional magnetic memory. This chapter presents a combination of analytical modelling and micromagnetic simulations, with the aim to present a comprehensive panorama of the physics of pinning of domain walls at modu- lations, when moved under the stimulus of a magnetic field or a spin-polarized current. For the sake of considering simple physics, we consider diameters of a few tens of nanometers at most, and accordingly domain walls of trans- verse type. Modeling with suitable approximations provides simple scaling laws, while simulations are more accurate, refining the results and defining the range of validity of the models. While pinning increases with the relative change of diameter, a key feature is the much larger efficiency of pinning at an increase of diameter upon considering current rather than field, due to the drastic decrease of current density related to the increase of diameter.
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Rythmes et flux des migrations

Rythmes et flux des migrations

À la fin du Régime français, une population migrante diverse venue de partout en France, avec l’accent sur l’ouest et sur les villes, s’était transformée en population coloniale dis[r]

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Les flux migratoires en Méditerranée

Les flux migratoires en Méditerranée

Pour ce qui concerne la régulation des flux de travailleurs par l’UE, rien n’existe jusqu’à maintenant. Des tentatives ont bien été faites, mais sans succès. La Commission a connu à ce sujet sa pire défaite dans le domaine justice et affaires intérieures : elle avait présenté une proposition de directive en 2001, mais le texte n’a jamais été approuvé par le Conseil des ministres et a finalement été retiré au début de l’année 2006. Quelque mois auparavant, en décembre 2005, la Commission avait transmis au Conseil un « Programme d’action relatif à l’immigration légale » qui incarne une nouvelle approche en la matière. Il s’agit d’une démarche visant à prendre en compte un contexte politique qui semble hostile à l’évolution d’une véritable politique de l’Union et formulant des propositions bien plus prudentes que celle de 2001. En effet, cette proposition envisageait de donner au niveau communautaire le pouvoir de fixer des règles s’appliquant à tout travailleur, et incroyable mais vrai, elle ne prévoyait la fixation de quotas par les Etats membres que dans des cas exceptionnels, la Commission pouvant adresser à ces derniers des opinions et des avis, le cas échéant, et pas plus.
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Mean-field dynamics for Ginzburg-Landau vortices with pinning and applied force

Mean-field dynamics for Ginzburg-Landau vortices with pinning and applied force

As noticed in Remark 8.8 (a), the question of determining the depinning rate at the depinning threshold is of particular interest. While obtaining a complete answer seems difficult due to the variety of possible dynamical behaviors, we consider the simplest situation when the depinning is due to the bifurcation of a unique stable fixed point into a stable periodic orbit. A square-root power law is then obtained under a non-degeneracy condition. An additional assumption is made for simplicity, which reduces the computation to a 1D setting (being then comparable to some explicit computations in [1, 50]). This assumption is satisfied for β = 0 and for a forcing F that is parallel to a coordinate axis when the pinning potential h has similar symmetries as in the example of Figure 4 (see indeed Figure 5 ). Yet, we believe that the same result holds in more general situations.
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Effect of Manganese Doping of BaSrTiO 3 on Diffusion and Domain Wall Pinning

Effect of Manganese Doping of BaSrTiO 3 on Diffusion and Domain Wall Pinning

Utilization of the hyperbolic law allows us to discern the di fferent components of the material’s complex permittivity. Thus it is shown that the contributions of domain wall motion (vibrations and displacements) are rather small compared to the lattice contribution. By dissociating the two contributions to the lattice permittivity, we show that an appropriate dopant rate considerably reduces low frequency di ffusion (by a fac- tor higher than ten) while diminishing high frequency losses at the same time. The addition of manganese also reduces the domain wall mobility by the creation of additional pinning centers and hence the contribution to the complex permittiv- ity and tunability. The doping corresponds to a hardening of the BST since the domain structure is stabilized, the domain wall pinning/unpinning is limited and the associated losses are reduced. Therefore reducing the domain wall contribution is then beneficial for decreasing the material’s dielectric losses since wall motion is a very dissipative phenomena. Doping with 1% of manganese thus is a compromise between reduc- ing the domain wall contribution (constituting only a small part of the permittivity) and maintaining a high tunability and low dielectric losses due to the lattice contribution which is responsible for the predominant part of the material’s overall properties.
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Physique des flux de matière

Physique des flux de matière

m -2 s -1 . Le flux de chaleur étant conservé, l'énergie moyenne des particules incidentes sur la paroi est plus basse en configuration divertor (<10 eV) qu'en configuration limiteur. Recyclage du carburant et des cendres de fusion Les ions (D, T ou He) provenant du plasma et impactant les tuiles du limiteur ou du divertor peuvent après neutralisation et selon leur énergie et leur angle d'incidence, soit être réfléchis vers le plasma avec une énergie proche de leur énergie incidente, soit pénétrer sous la surface de la tuile, dans son volume. Une partie des ions neutralisés implantés dans le volume peut rester piégée dans le matériau, l'autre partie pouvant diffuser vers la surface et être réémise vers le plasma, après une étape de recombinaison moléculaire en surface pour D et T. Ces atomes et molécules qui quittent la paroi après migration dans le volume ont une énergie proche de la température de la paroi. Cet échange permanent de particules entre le plasma et la paroi est nommé recyclage et est un paramètre important pour le contrôle des décharges plasma. En effet, lorsqu’un matériau de tuile lie fortement (chimiquement) un ion incident neutralisé (cas des tuiles en carbone) ou qu'il favorise sa diffusion dans le volume (cas de certains métaux tel que le tungstène) il a un effet pompant. Ce pompage par la paroi favorise les décharges à haute performance et l'accession au mode H , dans lequel sont opérés la plupart des tokamaks actuels, mais la rétention de l'isotope radioactif de l'hydrogène T par les composants de la paroi doit être contrôlée pour ne pas dépasser la limite autorisée par l’Autorité de Sûreté Nucléaire. De même que la répartition des flux sur la paroi des tokamaks est très inhomogène, le recyclage peut largement varier d'un endroit à l'autre du réacteur, dans l’espace et dans le temps, certains composants en contact avec le plasma pouvant s'avérer pompant ou dégazant suivant les conditions locales de flux de particules et de température.
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Comparison of Pinning Voltage Estimation Methods in Pinned Photodiode CMOS Image Sensors

Comparison of Pinning Voltage Estimation Methods in Pinned Photodiode CMOS Image Sensors

foundation of V pin estimation methods used in the CIS com- munity. In particular, it is shown that some methods provide arbitrary V pin values, which depend on the experimental set- up. Moreover this study showed that the commonly accepted theoretical definition of the pinning voltage does not corre- spond to the physical parameter which is measured with the existing methods. This study is supported by both TCAD simulations and experimental data.

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On the Lyapunov exponent of random transfer matrices and on pinning models with constraints

On the Lyapunov exponent of random transfer matrices and on pinning models with constraints

Nous nous penchons ici sur deux versions désordonnées très particulières du modèle d’Ising (au sens où la géométrie du désordre est spécifique) pour lesquels l’énergie libre associée s’e[r]

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Production de chaleur, flux de chaleur et flux de géo-neutrinos dans les environs de SNOLAB

Production de chaleur, flux de chaleur et flux de géo-neutrinos dans les environs de SNOLAB

We co mpare estimates of crustal heat production in t he Sudbury region fr om airborne radiometrie surveys, from measurements on core samples from mining expl oration drill ho[r]

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Capillary pinning and blunting of immiscible gravity currents in porous media

Capillary pinning and blunting of immiscible gravity currents in porous media

h c =H scales linearly with Bo 21 5ðc=dÞ=ðDqgHÞ (Figure 3). After the dense wetting current reaches the left boundary of the flow cell, the bottom of the vertical pinned interface starts to depin and becomes part of the imbibition front. This results in a reduced vertically pinned interface. Since the amount of capillary pressure hysteresis in the system remains the same, the hydrostatic pressure increase along the now reduced vertical pinned interface only accounts for part of the entry- pressure difference between drainage and imbibition. At the pore scale, this is reflected by the larger radius of curvature at the top of the vertical pinned interface compared to that at the end of the exchange flow stage (Figure 4b). To balance capillary pressure hysteresis, the pinned interface moves upward and extends into the drainage front. The depinning of the previously pinned interface and the pinning of the previously draining interface are synchronized with each other such that the height difference between the top and the bottom of the pinned interface is always the same, Dh c . Eventually, the current stops when the entire
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LES FLUX MIGRATOIRES EN MÉDITERRANéE

LES FLUX MIGRATOIRES EN MÉDITERRANéE

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignemen[r]

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Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing

Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing

neighboring nanoplatelets (<100 Oe, see Sec. II B ) or the fields used to drive domain wall motion ( 1 kOe at most). B. Domain wall pinning A domain wall moving in a region of the continuous layer that is located beneath an array will be subject to two sources of pinning. The first source of pinning arises from an interac- tion between the domain wall and the random, weak disorder that is intrinsic to continuous Pt/Co layers. 24 , 25 This leads to the thermally activated creep dynamics that are typically observed in such films. 24 , 25 , 33 , 36 , 37 The second source of pin- ning arises from the dipolar field generated by the nanoplate- lets, which can locally impede domain wall motion. 22 In the following, we discuss how the nanoplatelets’ stray dipolar fields can locally aid or counteract the effect of the applied field which is always perpendicular to the film plane.
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