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.
