https://doi.org/10.1140/epjb/e20020092
MO analysis of macroscopic supercurrent flow in MgB2
1
INFM - U.d.R Torino-Politecnico; INFN - Sez. Torino; Politecnico di Torino, c.so Duca degli Abruzzi 24, 10129 Torino, Italy
2
Edison S.p.A, Foro Buonaparte 31, 20121 Milano, Italy
Corresponding author: a mezzetti@polito.it
Received:
31
May
2001
Revised:
5
December
2001
Published online: 15 April 2002
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis. A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration, at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a network of strongly coupled Josephson junctions.
PACS: 74.70.-b – Superconducting materials (excluding high-Tc compounds) / 74.50.+r – Proximity effects, weak links, tunneling phenomena, and Josephson effects / 74.80.-g – Spatially inhomogeneous structures
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002