Fluxon dynamics by microwave surface resistance measurements in MgB2

Gallitto, Aurelio Agliolo; Bonura, Marco; Fricano, S.; Vigni, M. Li; Giunchi, G.

doi:10.1016/j.physc.2003.09.103

Cited by 3 publications

(2 citation statements)

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“…As already mentioned, results very similar to those reported in this paper have been obtained in all the MgB 2 bulk samples we have investigated [11][12][13], except in a strongly irradiated MgB 2 bulk sample, in which the two gaps merged into a single value [11]. Moreover, the anomalous plateau in the decreasing-field branch of the R s (H 0 ) curve has not been observed in samples of MgB 2 consisting of fine powder [13].…”

Section: Analysis Of the Resultssupporting

confidence: 89%

“…Studies reported in the literature on the field-induced variations of R s in MgB 2 have highlighted several anomalies, especially at applied magnetic fields much lower than the upper critical field, among which are unusually enhanced field-induced mw losses [8][9][10][11] and a magnetic hysteresis of unconventional shape [11][12][13]. It has been suggested that these anomalies are strictly related to the peculiarities of the fluxon lattice in MgB 2 .…”

Section: Introductionmentioning

confidence: 99%

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Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB₂at temperatures nearT_c

Bonura

Gallitto

Vigni

et al. 2009

Supercond. Sci. Technol.

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We report on the magnetic-field-induced variations of the microwave surface resistance, R s , in a polycrystalline MgB 2 sample, at different values of temperature. We have detected a magnetic hysteresis in R s , which exhibits an unexpected plateau on decreasing the DC magnetic field below a certain value. In particular, at temperatures near T c the hysteresis manifests itself only through the presence of the plateau. Although we do not quantitatively justify the anomalous shape of the magnetic hysteresis, we show that the results obtained in the reversible region of the R s (H) curve can be quite well accounted for by supposing that, in this range of magnetic field, the π gap is almost suppressed by the applied field and, consequently, all the π-band charge carriers are quasiparticles. On this hypothesis, we have calculated R s (H) supposing that fluxons assume a conventional (single core) structure and the flux dynamics can be described in the framework of conventional models. From the fitting of the experimental results, we determine the values of H π c2 (T) at temperatures near T c. In our opinion, the most important result of our investigation is that, at least at temperatures near T c , the value of the applied field that separates the reversible and irreversible regions of the R s (H) curves is just H π c2 (T); a qualitative discussion of the possible reasons for this finding is given.

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Section: Analysis Of the Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB₂at temperatures nearT_c

Bonura

Gallitto

Vigni

et al. 2009

Supercond. Sci. Technol.

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Depinning frequency in a heavily neutron-irradiated MgB2 sample

Bonura

Gallitto

Vigni

et al. 2008

Physica C: Superconductivity and its Applications

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The 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, ω 0 , at different values of the temperature. Although the pinning is not particularly effective, the value of ω 0 obtained at low temperatures is considerably higher than that observed in conventional low-temperature superconductors.

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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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Fluxon dynamics by microwave surface resistance measurements in MgB2

Cited by 3 publications

References 12 publications

Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB₂at temperatures nearT_c

Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB₂at temperatures nearT_c

Depinning frequency in a heavily neutron-irradiated MgB2 sample

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

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Fluxon dynamics by microwave surface resistance measurements in MgB2

Cited by 3 publications

References 12 publications

Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB2at temperatures nearTc

Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB2at temperatures nearTc

Depinning frequency in a heavily neutron-irradiated MgB2 sample

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

Contact Info

Product

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Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB₂at temperatures nearT_c

Field-induced suppression of the π-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB₂at temperatures nearT_c