Irreversible magnetization in thin YBCO films rotated in external magnetic field

The magnetization M of a thin YBa₂Cu₃O₇-δ film is measured as a function of the angle θ between the applied field H and the c-axis. For fields above the first critical field, but below the Bean's field for first penetration H*, M(θ) is symmetric with respect to θ = π and the magnetization curves for forward and backward rotation coincide. For H > H* the curves are asymmetric and they do not coincide. These phenomena have a simple explanation in the framework of the Bean critical state model.