Ac field dependence of the susceptibility of Bi2Sr2CaCu2O8 thin films at low dc fields

We have measured the ac field dependence of the ac susceptibility of 400 nm thick Bi2212 thin films at low dc fields 0 ≤μ0Ha ≤ 1 mT in transverse geometry. We show that at reduced temperaturest≤0.85 the ac field dependence can be described by the non-linear Bean model after Brandt as in Y123 thin films. Att>0.85, however, we observe a decrease of the energy dissipation and shielding capability. The critical current density at zero dc field is given byjc−4×1010(1−(T/Tc))2.8±0.1 A/m2.