Critical-state effects on microwave losses in type-II superconductors

Bonura, Marco; Gennaro, Emiliano Di; Gallitto, Aurelio Agliolo; Vigni, M. Li

doi:10.1140/epjb/e2006-00320-9

Cited by 18 publications

(39 citation statements)

References 26 publications

(54 reference statements)

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“…Microwave losses induced by static magnetic fields have been investigated by several authors [1][2][3][4][5][6][7][8][9]32,33]. At low temperatures and for applied magnetic fields lower enough than the upper critical field, the main contribution arises from the fluxon motion; however, it has been pointed out that a noticeable contribution can arise from the presence of normal fluid, especially at temperatures near T c and for magnetic fields of the same order of H c2 ðTÞ.…”

Section: Discussionmentioning

confidence: 99%

“…When fluxons are in the critical state, the assumption of uniform B is no longer valid and the CC theory does not correctly describe the field-induced variations of R s . Recently, we have investigated the field-induced variations of the mw surface resistance in superconductors in the critical state and have accounted for the magnetic hysteresis in the R s ðH 0 Þ curves [32,33]. The details of the procedure we have followed to account for the experimental results of Fig.…”

Section: ð1þmentioning

confidence: 99%

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Magnetic hysteresis in the microwave surface resistance of Nb samples in the critical state

2006

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a b s t r a c tThe magnetic-field-induced variations of the microwave surface resistance have been investigated in a heavily neutron-irradiated MgB 2 sample, in which the irradiation has caused the merging of the two gaps into a single value. The experimental results have been analyzed in the framework of the Coffey and Clem model. By fitting the experimental data, we have determined the field dependence of the depinning frequency, x 0 , at different values of the temperature. Although the pinning is not particularly effective, the value of x 0 obtained at low temperatures is considerably higher than that observed in conventional low-temperature superconductors.

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Section: Discussionmentioning

confidence: 99%

Section: ð1þmentioning

confidence: 99%

Magnetic hysteresis in the microwave surface resistance of Nb samples in the critical state

2006

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“…Microwave losses induced by static magnetic fields have been investigated by several authors [27,28,29,30,31,32,42,48]. At low temperatures and for applied magnetic fields lower enough than the upper critical field, the main contribution arises from the fluxon motion; however, it has been pointed out that a noticeable contribution can arise from the presence of normal fluid, especially at temperatures near T c and for magnetic fields of the same order of H c2 (T ).…”

Section: The Modelmentioning

confidence: 99%

“…1a), the effects of the nonuniform B distribution on R s are particularly enhanced because in the two surfaces of the sample normal to the external magnetic field the mw current and fields penetrate along the fluxon axis and, consequently, the mw losses involve the whole vortex lattice. However, in this case, one can easily take into account the non-uniform B distribution by calculating a proper averaged value of R s over the whole sample as follows [42,48] …”

Section: The Modelmentioning

confidence: 99%

Microwave surface resistance of pristine and neutron-irradiated MgB2 samples in magnetic field

et al. 2008

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Abstract. We report on the microwave surface resistance of two polycrystalline Mg 11 B2 samples; one consists of pristine material, the other has been irradiated at very high neutron fluence. It has already been reported that in the strongly irradiated sample the two gaps merge into a single value. The mw surface resistance has been measured in the linear regime as a function of the temperature and the DC magnetic field, at increasing and decreasing fields. The results obtained in the strongly irradiated sample are quite well justified in the framework of a generalized Coffey and Clem model, in which we take into account the field distribution inside the sample due to the critical state. The results obtained in the pristine sample show several anomalies, especially at low temperatures, which cannot be justified in the framework of standard models for the fluxon dynamics. Only at temperatures near Tc and for magnetic fields greater than 0.5Hc2(T ) the experimental data can quantitatively be accounted for by the Coffey and Clem model, provided that the upper-critical-field anisotropy is taken into due account. PACS

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“…Coffey and Clem (CC) have elaborated a comprehensive theory, in the framework of the two-fluid model of superconductivity [24], under the assumption that the induction field, B, is uniform within the AC-field penetration depth; so, it is valid for applied fields higher enough than the first-penetration field whenever the effects of the critical state can be neglected [36]. On the other hand, we do not observe magnetic hysteresis except in the field range in which the field-induced mw losses are mainly due to the presence of weak links.…”

Section: Field-induced Variation Of Rsmentioning

confidence: 99%

Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y1.6Ba2.3Cu3.3O7−x samples

Gallitto

Duca

Vigni

et al. 2012

Physica C: Superconductivity

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We report on the microwave surface resistance of melt-textured Y 1.6 Ba 2.3 Cu 3.3 O 7−x samples, doped with different amount of B 2 O 3 and, subsequently, irradiated by thermal neutrons at the fluence of 1.476 × 10 17 cm −2 . The microwave surface resistance has been measured as a function of temperature and DC magnetic field. The experimental results are quantitatively discussed in the framework of the Coffey and Clem theory, properly adapted to take into account the d-wave nature of cuprate superconductors. By fitting the experimental data at zero DC field, we have highlighted the effects of the induced defects in the general properties of the samples, including the intergranular region. The analysis of the results obtained at high DC fields allowed us to investigate the fluxon dynamics and deduce the depinning frequency; in particular, we have shown that the addition of B 2 O 3 up to 0.1 wt% increases the effectiveness of the defects to hinder the fluxon motion induced by the microwave current.

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Critical-state effects on microwave losses in type-II superconductors

Cited by 18 publications

References 26 publications

Magnetic hysteresis in the microwave surface resistance of Nb samples in the critical state

Magnetic hysteresis in the microwave surface resistance of Nb samples in the critical state

Microwave surface resistance of pristine and neutron-irradiated MgB2 samples in magnetic field

Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y1.6Ba2.3Cu3.3O7−x samples

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