The upper critical field in superconducting MgB2

Müller, K.‐H.; Fuchs, G.; Handstein, A.; Nenkov, K.; Narozhnyi, V. N.; Eckert, D.

doi:10.1016/s0925-8388(01)01197-5

Cited by 76 publications

(68 citation statements)

References 8 publications

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“…5 is their pronounced positive curvature near T c . Similar results have been already observed for non-textured MgB 2 samples [11,12]. Such a positive curvature of H c2 (T) near T c is a typical feature observed for the nonmagnetic rare-earth nickel borocarbides RNi 2 B 2 C (R=Y, Lu) and can be explained by taking into account the dispersion of the Fermi velocity using an effective two-band model for superconductors in the clean limit [13].…”

Section: Resultssupporting

confidence: 84%

Fully dense MgB2 superconductor textured by hot deformation

Handstein

Hinz

Fuchs

et al. 2001

Journal of Alloys and Compounds

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Bulk textured MgB 2 material of nearly full density showing a weak c-axis alignment of the hexagonal MgB 2 grains parallel to the pressure direction was obtained by hot deformation of a stoichiometric MgB 2 pellet prepared by a gas-solid reaction. The texture of the material was verified by comparing the x-ray diffraction patterns of the hot deformed material with isotropic MgB 2 powder. A small, but distinct anisotropy of the upper critical field up to ∼ 1.2 depending on degree of texture was found by resistance and susceptibility measurements. No anisotropy of the critical current density determined from magnetization measurements was found for the textured material.

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Section: Resultssupporting

confidence: 84%

Fully dense MgB2 superconductor textured by hot deformation

Handstein

Hinz

Fuchs

et al. 2001

Journal of Alloys and Compounds

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“…We find that dH c2 /dT=5100 Gauss/K near T c which is comparable to that found by Larbalestier et al (~5000 Gauss/K) [31] and slightly greater than that found by Finnemore et al (4400 Gauss/K) [30]. However, other studies have found that H c2 =H c2 *(1-T/T c ) 1+α where α can be 0.25 or greater [23,[27][28][29]. It has been stated that a positive curvature is also observed in the rare-earth nickel borocarbides, where it has been attributed to an effective two-band model for superconductors in the clean limit [27].…”

Section: Results and Analysissupporting

confidence: 81%

“…However, other studies have found that H c2 =H c2 *(1-T/T c ) 1+α where α can be 0.25 or greater [23,[27][28][29]. It has been stated that a positive curvature is also observed in the rare-earth nickel borocarbides, where it has been attributed to an effective two-band model for superconductors in the clean limit [27]. However, as mentioned earlier, a far infrared study provided evidence that MgB 2 is in the dirty limit [41].…”

Section: Results and Analysismentioning

confidence: 94%

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Magnetization and microwave study of superconductingMgB2

et al. 2002

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We report magnetic field dependent magnetization and microwave impedance measurements on a MgB 2 superconductor prepared by high pressure synthesis. We find that the upper critical field is linearly dependent on temperature near T c and the dc irreversibility field exponent is ~1.4. The microwave data display an excess surface resistance below T c which is neither observed in low T c nor in high temperature superconductors (HTSC). The real part of the complex conductivity, σ 1 , shows a huge maximum below T c and the imaginary part, σ 2 , is linear for temperatures less than 20 K, which can not be simply accounted for by the weak coupling BCS model with an s-wave superconducting order parameter. We speculate that this may be due to the two gaps reported by other studies.Unlike measurements on the high temperature superconducting cuprates, we find no evidence of weak-links in the superconducting state. By inverting the magnetic field dependent impedance data, we find a vortex depinning frequency that decreases with increasing magnetic field and evidence for an anisotropic upper critical magnetic field.

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“…Critical current densities on the order of 10 4 to 10 5 A/cm 2 have been reported by several groups for polycrystalline MgB 2 bulk samples [2][3][4][5][6][7][8]. A strong link type critical current density has been observed, regardless of the degree of grain alignment [3].…”

Section: Introductionmentioning

confidence: 95%

Fast formation and superconductivity of MgB2 thick films grown on stainless steel substrate

Wang

Ionescu

et al. 2001

Physica C: Superconductivity

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The fabrication, characterisation, and superconductivity of MgB 2 thick films grown on stainless steel substrate were studied. XRD, SEM, and magnetic measurements were carried out. It was found that the MgB 2 thick films can be fast formed by heating samples to 660 o C then immediately cooling down to room temperature. XRD shows above 90% MgB 2 phase and less than 10 % MgO. However, the samples sintered at 800 o C for 4 h contain both MgB 4 and MgO impurities in addition to MgB 2 . The fast formed MgB 2 films appear to have a good grain connectivity that gives a J c of 8 x 10 4 A/cm 2 at 5 K and 1 T and maintained this value at 20 K in zero field.2

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The upper critical field in superconducting MgB2

Cited by 76 publications

References 8 publications

Fully dense MgB2 superconductor textured by hot deformation

Fully dense MgB2 superconductor textured by hot deformation

Magnetization and microwave study of superconductingMgB2

Fast formation and superconductivity of MgB2 thick films grown on stainless steel substrate

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