Search results for "Microwave surface resistance"

showing 10 items of 11 documents

Electromagnetic response of LaO_0.94F_0.06FeAs: AC susceptibility and microwave surface resistance

2009

We discuss on the electromagnetic response of a polycrystalline sample of LaO_0.94F_0.06FeAs exposed to DC magnetic fields up to 10 kOe. The low- and high-frequency responses have been investigated by measuring the AC susceptibility at 100 kHz and the microwave surface resistance at 9.6 GHz. At low as well as high DC magnetic fields, the susceptibility strongly depends on the amplitude of the AC driving field, highlighting enhanced nonlinear effects. The field dependence of the AC susceptibility exhibits a magnetic hysteresis that can be justified considering the intragrain-field-penetration effects on the intergrain critical current density. The microwave surface resistance exhibits a cloc…

LaOFFeAs superconductor; Electromagnetic response; AC susceptibility; Microwave surface resistanceSuperconductivityHistoryMaterials scienceCondensed matter physicsField (physics)Condensed Matter - SuperconductivityLaOFFeAs superconductorElectromagnetic responseField dependenceFOS: Physical sciencesAstrophysics::Cosmology and Extragalactic AstrophysicsMagnetic hysteresisComputer Science ApplicationsEducationMagnetic fieldSuperconductivity (cond-mat.supr-con)AmplitudeAC susceptibilityMicrowave surface resistanceLattice (order)Condensed Matter::SuperconductivityCrystallite
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Frequency dependence of the microwave surface resistance of MgB2 by coaxial cavity resonator

2014

Abstract We report on the microwave (mw) properties of a cylindrical MgB2 rod prepared by the reactive liquid Mg infiltration technology. The MgB2 rod, 94.3 mm long, is used as inner conductor of a coaxial cavity having a Cu tube as external conductor. By analyzing the resonance curves of the cavity in the different resonant modes and at different temperatures, we have determined the temperature dependence of the mw surface resistance, R s , of the MgB2 material, at fixed frequencies, and the frequency dependence of R s , at fixed temperatures. Our results show that the R s ( f ) curves follow a f n law, where n decreases on increasing the temperature, starting from n ≈ 2 , at T = 4.2 K , d…

Materials scienceMgB2 superconductorSuperconducting cavity resonatorSettore FIS/01 - Fisica SperimentaleMagnesium diborideEnergy Engineering and Power TechnologySuperconducting cavity resonator; Magnesium diboride; Microwave surface resistanceCondensed Matter PhysicsElectronic Optical and Magnetic MaterialsConductorResonatorchemistry.chemical_compoundCoaxial cavity resonatorchemistryCoaxial cavityMicrowave surface resistanceExcited stateQuasiparticleMagnesium diborideElectrical and Electronic EngineeringAtomic physicsMicrowaveSheet resistancePhysica C: Superconductivity and its Applications
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Fluxon dynamics in Li–Al codoped MgB2 by microwave surface resistance measurements

2010

The magnetic-field-induced variations of the microwave surface resistance, Rs, have been investigated in ceramic Mg_(1-x)(LiAl)_xB_2, with x in the range 0.1 - 0.4. The measurements have been performed on increasing and decreasing the DC magnetic field, H0, at fixed temperatures. At low temperatures, we have observed a magnetic hysteresis in the Rs(H0) curves in all the investigated samples. On increasing the temperature, the range of H0 in which the hysteretic behavior is visible shrinks; however, in the sample with x=0.1 it is present up to temperatures close to Tc. We show that the field dependence of Rs can be quantitatively justified taking into account the critical-state effects on th…

MgB2 superconductorMicrowave surface resistanceMgB2 superconductor; Fluxon dynamics; Microwave surface resistanceFluxon dynamic
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Anomalous hysteretic behaviour of the microwave surface resistance in MgB2 superconductor

2007

MgB2 superconductormicrowave surface resistanceSettore FIS/01 - Fisica Sperimentale
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Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y1.6Ba2.3Cu3.3O7−x samples

2012

We report on the microwave surface resistance of melt-textured Y_1.6Ba_2.3Cu_3.3O_7-x samples, doped with different amount of B_2O_3 and, subsequently, irradiated by thermal neutrons at the fluence of 1.476 \times 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.…

SuperconductivityB2O3 additionMaterials scienceCondensed matter physicsFluxonCondensed Matter - SuperconductivitySettore FIS/01 - Fisica SperimentaleDopingFOS: Physical sciencesEnergy Engineering and Power TechnologyThermal-neutron irradiationCondensed Matter PhysicsFluenceNeutron temperatureElectronic Optical and Magnetic MaterialsMagnetic fieldSuperconductivity (cond-mat.supr-con)Depinning frequency; Microwave surface resistance; Thermal-neutron irradiationCondensed Matter::SuperconductivityMicrowave surface resistanceCuprateDepinning frequencyElectrical and Electronic EngineeringMicrowavePhysica C: Superconductivity
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Depinning frequency in a heavily neutron-irradiated MgB2 sample

2008

The magnetic-field-induced variations of the microwave surface resistance have been investigated in a heavily neutron-irradiated MgB2 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, omega_0, at different values of the temperature. Although the pinning is not particularly effective, the value of omega_0 obtained at low temperatures is considerably higher than that observed in conventional low-temperature superconductors.

SuperconductivityFlux pinningMaterials scienceCondensed matter physicsBand gapCondensed Matter - Superconductivitysuperconductivity microwave surface resistance mgb2CRITICAL-STATEEnergy Engineering and Power TechnologyField dependenceFOS: Physical sciencesII SUPERCONDUCTORSCondensed Matter PhysicsSample (graphics)RF MAGNETIC-PERMEABILITYElectronic Optical and Magnetic MaterialsSuperconductivity (cond-mat.supr-con)Surface conductivityTEMPERATURE-DEPENDENCECondensed Matter::SuperconductivityNeutronIrradiationElectrical and Electronic EngineeringMICROWAVE SURFACE-RESISTANCE
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Microwave surface resistance of pristine and neutron-irradiated MgB2 samples in magnetic field

2008

We report on the microwave surface resistance of two polycrystalline Mg11B2 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 ob…

SuperconductivityMaterials scienceCondensed matter physicsFluxonCondensed Matter - SuperconductivityMIXED-STATECRITICAL-STATEFOS: Physical sciencesII SUPERCONDUCTORSCondensed Matter PhysicsElectronic Optical and Magnetic MaterialsMagnetic fieldSuperconductivity (cond-mat.supr-con)Superconductivity microwave surface resistance mgb2POINT-CONTACT SPECTROSCOPYNeutron fluxNeutronSINGLE-CRYSTALSIrradiationAnisotropySheet resistance
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Microwave Surface Resistance and Upper-Critical-Field Anisotropy of MgB2 Superconductor

2002

The field-induced variations of the microwave surface resistance are investigated in two different samples of powdered MgB2. The experimental results can be justified in the framework of the Coffey and Clem model with fluxons moving in the flux-flow regime, provided that the anisotropy of the upper critical field is taken into due account. Assuming the angular dependence of the upper critical field expected from the anisotropic Ginzburg-Landau theory, we determine the anisotropy factor by fitting the experimental data of the field dependence of the microwave surface resistance. We show that the anisotropy factor is constant in a range of temperatures of about 3 K below Tc and it takes on di…

SuperconductivityMicrowave surface resistanceRange (particle radiation)Materials scienceCondensed matter physicsCondensed Matter - SuperconductivityEnergy Engineering and Power TechnologyField dependenceFOS: Physical sciencesCondensed Matter PhysicsElectronic Optical and Magnetic MaterialsSuperconductivity (cond-mat.supr-con)Condensed Matter::SuperconductivityAngular dependenceElectrical and Electronic EngineeringAnisotropyConstant (mathematics)Critical field
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Anomalous magnetic hysteresis in the microwave surface resistance of MgB2 superconductor

2007

We report experimental results of the field-induced variations of the microwave surface resistance in samples of MgB2, produced by different methods. By sweeping the DC magnetic field at increasing and decreasing values, we have detected a magnetic hysteresis that can be ascribed to the different magnetic induction, due to the critical state of the fluxon lattice. The hysteresis observed in the bulk samples has an unusual shape, which cannot be justified in the framework of the critical-state models.

SuperconductivitySuperconductivityHistoryMicrowave surface resistanceMaterials scienceCondensed matter physicsFluxonMgB2Condensed Matter - SuperconductivitySettore FIS/01 - Fisica SperimentaleFOS: Physical sciencesMagnetic hysteresismicrowave surface impedanceComputer Science ApplicationsEducationElectromagnetic inductionMagnetic fieldSuperconductivity (cond-mat.supr-con)Lattice (order)Bulk samplesCondensed Matter::Superconductivity
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Field-induced suppression of the pi-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB_2 at temperatures near …

2009

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 pi-gap is almost supp…

SuperconductivitySuperconductivityMaterials scienceCondensed matter physicsField (physics)Condensed Matter - SuperconductivityMetals and AlloysFOS: Physical sciencesCondensed Matter PhysicsPlateau (mathematics)Magnetic hysteresisMagnetic fieldSuperconductivity (cond-mat.supr-con)HysteresisMicrowave surface resistanceCondensed Matter::SuperconductivityMaterials ChemistryCeramics and CompositesQuasiparticleCharge carrierElectrical and Electronic EngineeringSuperconductivity; Microwave surface resistance;
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