Geometric barrier in Bi₂Sr₂CaCu₂O_7+δ single crystals

In this paper we present isothermal magnetization curves measured by using a Bi₂Sr₂CaCu₂O_7+δ single crystal in the temperature range 50 K–80 K, for external magnetic fields applied along the sample thickness. The experimental data is compared with the numerically calculated magnetization, in which the specimen geometry is correctly taken into account. In this calculation an explicit equilibrium relation H=H(B,κ̃) is also considered, where κ̃ is related to the Ginzburg-Landau parameter. The reversible experimental and calculated magnetizations show good agreement, allowing us to estimate H_c1(T). The results show that the geometric barrier is mainly responsible for the magnetic hysteresis observed at high temperatures (T>~70 K) where bulk pinning is negligible.