Magnetic relaxation in a superconducting plate with rotating flux lines

Magnetic relaxation in a superconducting plate placed in an external magnetic field parallel to its plane is analyzed in the following situation: The external field is switched on and then rotated through some angle in the plane of the plate without changing its magnitude, and then its magnitude and direction are kept fixed. Since the rotation causes flux-line cutting, the so-called general critical state is established in the sample. The relaxation of just this state is investigated. We find expressions for the electric fields and relaxation rates of the magnetic field components and currents in the plate. It is shown that study of the magnetic flux decay allows one to extract the effective height of the activation barrier against flux-line cutting from experimental data.