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Pissas, M.; Moraitakis, E.; Σταμόπουλος, Δ.; Papavassiliou, George C.; Psycharis, V.; Koutandos, Spiros

doi:10.1023/a:1012944216895

Cited by 42 publications

(30 citation statements)

References 22 publications

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“…3 indicate that the strong bulk pinning previously reported for polycrystalline 24 and thin films 4 might be due to entirely extrinsic pinning sites, such as grain boundaries and crystallographic defects. 25 This is consistent with the absence of core pinning, even at Tϳ0.5ϫT c , for bulk sample. 5…”

Section: B Magnetic Propertiessupporting

confidence: 83%

Microstructure and pinning properties of hexagonal-disc shaped single crystallineMgB2

et al. 2002

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We synthesized hexagonal-disc-shaped MgB 2 single crystals under high-pressure conditions and analyzed the microstructure and pinning properties. The lattice constants and the Laue pattern of the crystals from x-ray micro-diffraction showed the crystal symmetry of MgB 2 . A thorough crystallographic mapping within a single crystal showed that the edge and c axis of hexagonal-disc shape exactly matched the ͓1010͔ and the ͓0001͔ directions of the MgB 2 phase. Thus, these well-shaped single crystals may be the best candidates for studying the direction dependences of the physical properties. The magnetization curve and the magnetic hysteresis curve for these single crystals showed the existence of a wide reversible region and weak pinning properties, which supported our single crystals being very clean.

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Section: B Magnetic Propertiessupporting

confidence: 83%

Microstructure and pinning properties of hexagonal-disc shaped single crystallineMgB2

et al. 2002

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“…On the other hand, currently available theories distinguish the driving mechanisms of TMI when observed in thin films or in bulk samples. In order to directly compare the two cases, we also present magnetic measurements performed in a bulk sample of MgB 2 superconductor [37]. The preparation process is reported elsewhere [38].…”

Section: Resultsmentioning

confidence: 99%

“…In order to directly compare the two cases, we also present magnetic measurements performed in a bulk sample of MgB 2 superconductor [37]. The preparation process is reported elsewhere [38]. In fig.…”

Section: Resultsmentioning

confidence: 99%

From the second magnetization peak to peak effect. A study of superconducting properties in Nb films and MgB₂bulk samples

Σταμόπουλος¹,

Speliotis²,

Niarchos³

2004

Supercond. Sci. Technol.

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We report on magnetic and magnetoresistance measurements in two categories of superconducting Nb films grown via magnetron sputtering and MgB−2 bulk samples. In the first category, films of Tc = 9.25 K were produced by annealing during deposition. In these films, the magnetic measurements exhibited the so-called "second magnetization peak" ("SMP"), which is accompanied by thermomagnetic instabilities (TMI). The characteristic field H fj , where the first flux jump occurs, has been studied as a function of the sweep rate of the magnetic field. Interestingly, in the regime T < 6.4 K, the respective line H fj (T ) is constant, H fj (T< 6.4 K)= 40 Oe. A comparison to TMI observed in MgB2 bulk samples is also performed. Our experimental findings can't be described accurately by current theories on TMI. In the second category, films of Tc = 8.3 K were produced without annealing during deposition. In such films, we observed a peak effect (PE). In high magnetic fields the PE is accompanied by a sharp drop and a narrow hysteretic behavior (∆T < 20 mK) in the measured magnetoresistance. In contrast to experimental works presented in the past, the comparison of our magnetic measurements with the magnetoresistance data suggests that rather the appearance of surface superconductivity than the melting transition of vortex matter, is the cause of the observed behavior.

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“…According to the Burlachkov theory [7], the initial stage of the magnetic relaxation should be determined by the weakest one of the two sources of magnetic irreversibility: the bulk pinning and the surface barrier. It has been shown that the magnetic hysteresis loops of powdered MgB 2 samples show asymmetric behavior in the two branches at increasing and decreasing fields [4,10], suggesting that the surface barrier controls the magnetic irreversibility. The results have been ascribed to the weakness of the bulk pinning in the powder [4]; so, the logarithmic decay of the SH signal could be ascribed to fluxcreep processes, which occur at short times because of the weak bulk pinning.…”

Section: Discussionmentioning

confidence: 99%

“…Interaction between magnetic flux and sample surface has mainly been studied by magnetization measurements [1][2][3][4]. Surface-barrier effects manifest themselves in: i) first-penetration field, H p , higher than the lower critical field, H c1 ; ii) hysteresis loop of the magnetization curve asymmetric in the two branches at increasing and decreasing fields; iii) magnetic relaxation rates different for flux entry and exit.…”

Section: Introductionmentioning

confidence: 99%

Time evolution of the microwave second-harmonic response of MgB2 superconductor

Gallitto

Vigni

Vaglica

2004

Physica C: Superconductivity

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We report on transient effects in the microwave second-order response of two ceramic MgB 2 samples. The time evolution of the second-harmonic signal is investigated for about 500 s after the sample has been exposed to a variation of the dc magnetic field. We suggest that during the first seconds the response is determined by diffusive motion of fluxons, while in the time scale of minutes it is ruled by magnetic relaxation over the surface barrier.

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Untitled

Cited by 42 publications

References 22 publications

Microstructure and pinning properties of hexagonal-disc shaped single crystallineMgB2

Microstructure and pinning properties of hexagonal-disc shaped single crystallineMgB2

From the second magnetization peak to peak effect. A study of superconducting properties in Nb films and MgB₂bulk samples

Time evolution of the microwave second-harmonic response of MgB2 superconductor

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Untitled

Cited by 42 publications

References 22 publications

Microstructure and pinning properties of hexagonal-disc shaped single crystallineMgB2

Microstructure and pinning properties of hexagonal-disc shaped single crystallineMgB2

From the second magnetization peak to peak effect. A study of superconducting properties in Nb films and MgB2bulk samples

Time evolution of the microwave second-harmonic response of MgB2 superconductor

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Product

Resources

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From the second magnetization peak to peak effect. A study of superconducting properties in Nb films and MgB₂bulk samples