A scaling law for ac susceptibility of an YBa2Cu3O film in a perpendicular ac field

Abstract

The ac susceptibility (ACS) of an YBa2Cu3O thin film in a perpendicular ac magnetic field (Ha) from 0.22 to 30.8 G is measured as a function of temperature. The temperature dependence of the real (χ′) and imaginary (χ′′) parts of the ACS for various Ha can be well scaled onto a single curve using the peak value (χp″) and temperature (Tp) of χ′′(T) as the scaling parameters. The scaling law suggests that the critical state can be established only below Tp. Above Tp, the ACS is determined by the screening effect of the film due to the sharp decrease of its resistance. Below Tp, the scaling behavior is in agreement with the theoretical approaches based on the critical state model, only if the temperature for zero critical current density is related to the irreversibility temperature Tirr rather than Tc. From the scaling law, we found that Tirr=Tp.