Study of magnetization and pinning mechanisms in MgB₂thin film superconductors: effect of heavy ion irradiation

Abstract

We report magnetization studies on MgB2 superconducting thin films in a temperature range 4.2–40 K and magnetic field range 0–6 T. Thin films prepared by both pulsed laser deposition (PLD) and electron beam evaporation (EBE) methods were investigated. In addition, both films were studied before and after heavy ion irradiation by 200 MeV Ag ions with a dose of 1011 ions cm−2. Variation of sweep rates during the measurement of the magnetization loop reveals the presence of flux creep in both films. The PLD film, after irradiation, shows a severe degradation of Tc, critical current densities (Jc) in low fields and irreversibility line (B*(T)). In contrast, the EBE film shows a slight enhancement in Tc, and nearly no change in Jc(B) and the position of irreversibility line after irradiation. For both pristine films, the obtained volume pinning forces Fp versus reduced field b = B/B* shows a good scaling for T ≤ 10 K, which matches well with the theoretical curve based on the flux line shear (FLS) pinning model. These and other results can be interpreted in terms of grain boundaries in MgB2 films acting as FLS channels.

Calculation of the volume pinning force inMgB2superconductors

“…The position of the peak field only shifts by about 3% from 0.341 for the clean to 0.352 for the dirty material. This difference is smaller than the usual deviations from the predicted behavior in textured MgB 2 superconductors ͑films͒, 14,43,44 which should be identical to that of isotropic superconductors ͑B / B irr = 0.2 for grain boundary pinning͒.…”

Charged Particle Irradiation Studies on Bismuth Based High Temperature Superconductors and MgB2: a comparative study

“…In MgB 2 , the irradiation studies with heavy ions on thin films [39] and protons on bulk materials [40] have not reflected any significant changes in T c and other superconducting properties. Hence we employed heavy ions like Neon with large deposition energy and high values of displacements per atom (dpa) to bring about changes in bulk samples.…”

Effect of vortex-vortex interactions on the critical current density of single-crystalline MgB2 thin films

“…Numerous results have been reported to enhance the J c in MgB 2 wires, tapes, and single crystals through heavy-ion irradiation and chemical doping [9,10]. These methods were also carried out on MgB 2 thin films, but even high energy ion irradiation could not improve the J c significantly [11], carbon doping was shown to decrease the selffield J c , although it is effective at high fields [12]. Therefore, a complete understanding of the flux pinning properties in high-quality MgB 2 thin films should be done, which could be a big aid in improving its J c .…”