Characterization of high-temperature superconductors by AC susceptibility measurements

Gömöry, Fedor

doi:10.1088/0953-2048/10/8/001

Cited by 286 publications

(211 citation statements)

References 232 publications

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“…The characteristic frequency for pinning effects, ω C , is independent of magnetic field in macroscopic samples, according to Eq. (13). The weak field dependence of ω p may be still consistent with this result (the effective κ p may depend on the number and distribution of vortices inside the sample in this hypothetic case of "confinement potential").…”

Section: A Frequency Dependencesupporting

confidence: 71%

“…4,5,6,7,8,9,10,11,12,13,14 The microwave surface impedance Z s = R s − iX s and the ac magnetic susceptibilityχ = χ ′ + iχ ′′ have been extensively studied. 1,2,3,4,5,6,7,8,9,10,11,12,13,14 Interesting behavior has been found for different values of the frequency, the magnetic field, the pinning force and the thermal fluctuations, 4,5,6,7 whereas linear and nonlinear response appear depending on the strength of the ac signal. 7 The main interest so far has been on the electrodynamics of macroscopic samples containing a large number of vortices.…”

Section: Introductionmentioning

confidence: 99%

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ac magnetic response of mesoscopic type-II superconductors

Hernandez

Domı́nguez

2002

Phys. Rev. B

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The response of mesoscopic superconductors to an ac magnetic field is numerically investigated on the basis of the time-dependent Ginzburg-Landau equations (TDGL). We study the dependence with frequency ω and dc magnetic field H dc of the linear ac susceptibility χ(H dc , ω) in square samples with dimensions of the order of the London penetration depth. At H dc = 0 the behavior of χ as a function of ω agrees very well with the two fluid model, and the imaginary part of the ac susceptibility, χ"(ω), shows a dissipative a maximum at the frequency νo = c 2 /(4πσλ 2 ). In the presence of a magnetic field a second dissipation maximum appears at a frequency ωp ≪ ν0. The most interesting behavior of mesoscopic superconductors can be observed in the χ(H dc ) curves obtained at a fixed frequency. At a fixed number of vortices, χ"(H dc ) continuously increases with increasing H dc . We observe that the dissipation reaches a maximum for magnetic fields right below the vortex penetration fields. Then, after each vortex penetration event, there is a sudden suppression of the ac losses, showing discontinuities in χ"(H dc ) at several values of H dc . We show that these discontinuities are typical of the mesoscopic scale and disappear in macroscopic samples, which have a continuos behavior of χ(H dc ). We argue that these discontinuities in χ(H dc ) are due to the effect of nascent vortices which cause a large variation of the amplitude of the order parameter near the surface before the entrance of vortices.

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Section: A Frequency Dependencesupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

ac magnetic response of mesoscopic type-II superconductors

Hernandez

Domı́nguez

2002

Phys. Rev. B

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“…From the Bean critical state model [6], it follows that the dip is directly related to a peak in J c . Measurements of the harmonics of the AC susceptibility (χ AC ) have been widely used to study magnetic properties [2,23,24,26,27], and in particular the vortex dynamics [27] in type II superconductors. If the magnetic response is linear, only the 1 st harmonics can be detected, whereas non-linear magnetic properties are associated to the existence of higher harmonics [6,27].…”

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confidence: 99%

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

et al. 2006

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We report additional experimental evidences about the presence of an universal behavior in the Field-Temperature Phase Diagram of Type II Superconductors. This behavior is characterized by a phase transition in the vortex matter between the disordered and the Bragg Glass phase. The experimental detection of a Peak Effect phenomenon has been proved to be strictly connected to the existence of this phase transition. In this paper, we show the first observation of a Peak Effect in the compound Nb 3 Sn, by using 1 st harmonics of the AC magnetic susceptibility. Peak Effect has been detected at fields between 3T and 13T, whereas it is not observable at higher fields. This seems to be in contrast with the theoretical predictions of such a phase transition at all fields and, therefore, with the predicted universality in the magnetic behavior of the Type II superconductors. Nevertheless, by measuring the 3 rd harmonics of the AC susceptibility, this phase transition has been detected up to our highest available field (19 T), thus demonstrating the necessity of the higher harmonics analysis in studying these topics and moreover proving the validity of the theoretical predictions. Magnetic flux penetrates a type II superconductor in form of vortices, which distribute in a regular lattice in absence of defects [1,2]. Defects affect the lattice ordering, but prevent the dissipations associated to the vortex movement [2]. An universal field-temperature phase diagram has been supposed for all the type II superconductors with point defects. In this phase diagram a transition in the vortex lattice has been predicted, between a disordered phase and the Bragg Glass Phase [3,4]. This latter is characterized by a quasi long range order and a perfect topological order, in which the vortex lattice stills survives despite the presence of the pinning [3], as it has also been experimentally evidenced [5]. The disordered phase has been supposed to be again a glass phase ("multidomain glass"), but with a topological disorder at the largest length scales [4]. The critical current density, J c [6], generally decreasing with increasing temperature and/or magnetic field [2], shows a local maximum, known as Peak Effect [7], when the Disordered/Bragg Phase transition occurs. For this reason, the observation of the Peak Effect has been widely used to detect this phase transition [3]. The Peak Effect has been evidenced in various classes of type II superconductors, e.g. low-T c [8][9][10][11][12], high-T c [13][14][15], boro-carbides [16] and MgB 2 [17]; however, it has not been observed in Nb 3 Sn up to the present day, to the best of our knowledge. Nb 3 Sn crystallizes in the A15 type structure and is actually the most used material in the manufacturing of superconducting magnets at very high fields [18]. In the present work, measurements have been performed on a high quality Nb 3 Sn single crystal, furnished by M. Toyota [19] (Dimensions ≈ 3 x 1.32 x 0.43 mm 3 ). The sample was characterized by T c = 18.2 K, ΔT c = 0.1 K, T m = 38.84 K. A valu...

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“…5(a) and 5(b), respectively. In a superconductor sample with strongly connected grains, the two peaks are merged [33]. As seen from Figs.…”

Section: Resultsmentioning

confidence: 85%

The effect of nanosized CoFe2O4 addition on the magnetic properties of GdBa2Cu3O7-δ using AC magnetic susceptibility measurements

et al. 2016

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Superconductor samples of type (CoFe 2 O 4 ) x GdBa 2 Cu 3 O 7δ (0≤x≤0.1) were synthesized by the conventional solid-state reaction technique, whereas nanosized CoFe 2 O 4 was prepared by co-precipitation method with grain size of about 8.5 nm. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE). The temperature dependence of real (  ) and imaginary (  ) components of AC magnetic susceptibility (ACMS) at different magnetic field amplitude (3-15 Oe) was investigated. The analysis of the temperature dependence of ACMS was performed using Bean critical state model. The values of the critical current density c J at T > p T ( p T is the inter-granular loss peak temperature) were calculated as a function of magnetic field and nanosized CoFe 2 O 4 content. It was found that the low nanosized CoFe 2 O 4 addition content (x = 0.01) improves the critical current density c J of Gd-123 superconducting phase. The observed variation of c J with temperature indicated that the weak links are changed from superconductornormal metal-superconductor (SNS) for free sample to superconductor-insulator-superconductor (SIS) type of junctions for samples added with nanosized CoFe 2 O 4 of x > 0.01. We also discussed the experimental results in the framework of the critical state model to estimate the effective volume fraction of the grains g f using Cole-Cole plots.

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Characterization of high-temperature superconductors by AC susceptibility measurements

Cited by 286 publications

References 232 publications

ac magnetic response of mesoscopic type-II superconductors

ac magnetic response of mesoscopic type-II superconductors

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

The effect of nanosized CoFe2O4 addition on the magnetic properties of GdBa2Cu3O7-δ using AC magnetic susceptibility measurements

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