Field-induced networks of weak-links: an experimental demonstration that the paramagnetic Meissner effect is inherent to granularity

Ortiz, W.A.; Lisboa‐Filho, Paulo Noronha; Passos, W. A. C.; Araújo‐Moreira, F. M.

doi:10.1016/s0921-4534(01)00610-4

Cited by 14 publications

(13 citation statements)

References 34 publications

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“…The same attributes are also presented by thin films of Nb, YBCO [9] and MgB [11] submitted to a perpendicular field. Newer results, taken with the film under the action of an applied audio-frequency oscillating field, revealed that the AC-susceptibility fluctuates when the field amplitude and frequency are above certain threshold limits [11].…”

Section: Introductionmentioning

confidence: 65%

“…MO images are not only visually impressive, but also sensitive to determine field intensity profiles across the dendrites [4]. Another sensitive technique to detect the magnetic dendritic state is SQUID magnetometry [8], [9]. In fact, when in the magnetic dendritic state, a superconducting thin film behaves as a typical granular superconductor, whose magnetic response includes both intragranular and intergranular contributions.…”

Section: Introductionmentioning

confidence: 99%

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Effects of small magnetic fields on the critical current of thin films

Passos

Lisboa‐Filho

Kang

et al. 2003

IEEE Trans. Appl. Supercond.

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Magnetic fields applied perpendicularly to superconducting thin films may produce dendritic patterns, where penetrated and Meissner regions coexist, as observed in Nb, YBCO and MgB 2 . Due to large demagnetizing factors in the perpendicular geometry, small fields may be enough to drive portions of the sample into the mixed state. Lack of symmetry and local defects might then permeate the dendritic mode. This mode, in turn, can be detected by AC-susceptibility measurements, since penetrated fingers act as intergranular material, which reveals itself in a characteristic manner.Films of a few hundred nanometers thick and millimeter lateral sizes, develop dendrites even when submitted to Earth's field, what drastically limits the critical current, . This contribution studies how this field-induced granularity is further affected by the action of excitation AC-fields of small magnitudes and audio-frequencies.

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Section: Introductionmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Effects of small magnetic fields on the critical current of thin films

Passos

Lisboa‐Filho

Kang

et al. 2003

IEEE Trans. Appl. Supercond.

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“…According to the current paradigm, paramagnetic Meissner effect (PME) can be related to the presence of π -junctions (Braunisch et al 1992, Li 2003, Kostic et al 1996, Ortiz et al 2001, Passos et al 2000, Lucht et al 1995, Li and D. Dominguez 2000 , either…”

Section: On the Origin Of Dynamic Reentrancementioning

confidence: 99%

Dynamical reentrance and geometry imposed quantization effects in Nb–AlO_x–Nb Josephson junction arrays

Araújo‐Moreira¹,

Sergeenkov²

2008

Supercond. Sci. Technol.

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Abstract. In this review, we report on different phenomena related to the magnetic properties of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays (2D-JJA) of both shunted and unshunted Nb-AlO x -Nb tunnel junctions. By employing mutual-inductance measurements and using a high-sensitive home-made bridge, we have thoroughly investigated (both experimentally and theoretically) the temperature and magnetic field dependence of complex AC susceptibility of 2D-JJA. After brief description of the measurements technique and numerical simulations method, we proceed to demonstrate that the observed dynamic reentrance (DR) phenomenon is directly linked to the value of the Stewart-McCumber parameter β C . By simultaneously varying the inductance related parameter β L , we obtain a phase diagram β C -β L (which demarcates the border between the reentrant and non-reentrant behavior) and show that only arrays with sufficiently large value of β C will exhibit the DR behavior. The second topic of this review is related to the step-like structure (with the number of steps n = 4 corresponding to the number of flux quanta that can be screened by the maximum critical current of the junctions) which has been observed in the temperature dependence of AC susceptibility in our unshunted 2D-JJA with β L (4.2K) = 30 and attributed to the geometric properties of the array. The steps are predicted to manifest themselves in arrays with β L (T) matching a "quantization" condition β L (0)=2π(n+1).In conclusion, we demonstrate the use of the scanning SQUID microscope for imaging the local flux distribution within our unshunted arrays.

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“…According to the current paradigm, paramagnetic Meissner effect (PME) [1][2][3][4][5][6] can be related to the presence of π-junctions [7], either resulting from the presence of magnetic impurities in the junction [8,9] or from unconventional pairing symmetry [10]. Other possible explanations of this phenomenon are based on flux trapping [11] and flux compression effects [12] including also an important role of the surface of the sample [3].…”

Section: Introductionmentioning

confidence: 99%

On the origin of reentrance in 2D Josephson junction arrays

2005

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A comparative study of the magnetic properties of shunted and unshunted two-dimensional Josephson junction arrays (2D-JJA) is presented. Using a singleplaquette approximation of the 2D-JJA model, we were able to successfully fit all our experimental data (for the temperature, AC and DC field dependencies of susceptibility) and demonstrate that the dynamic reentrance of AC susceptibility is directly linked to the value of the Stewart-McCumber parameter β C . Based on extensive numerical simulations, a phase diagram β C − β L is plotted which demarcates the border between the reentrant and non-reentrant behavior in the arrays.

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Field-induced networks of weak-links: an experimental demonstration that the paramagnetic Meissner effect is inherent to granularity

Cited by 14 publications

References 34 publications

Effects of small magnetic fields on the critical current of thin films

Effects of small magnetic fields on the critical current of thin films

Dynamical reentrance and geometry imposed quantization effects in Nb–AlO_x–Nb Josephson junction arrays

On the origin of reentrance in 2D Josephson junction arrays

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Field-induced networks of weak-links: an experimental demonstration that the paramagnetic Meissner effect is inherent to granularity

Cited by 14 publications

References 34 publications

Effects of small magnetic fields on the critical current of thin films

Effects of small magnetic fields on the critical current of thin films

Dynamical reentrance and geometry imposed quantization effects in Nb–AlOx–Nb Josephson junction arrays

On the origin of reentrance in 2D Josephson junction arrays

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Dynamical reentrance and geometry imposed quantization effects in Nb–AlO_x–Nb Josephson junction arrays