Size effect in anisotropic hard superconductors

The amplitude dependence of the relative AC losses q in anisotropic superco nducting plate-like samples has been studied experimentally and theoretical ly. Contrary to the isotropic case where there exists one maximum in the de pendence of q = chi" on me amplitude h(0) of the AC magnetic field, two max ima in the dependence q(h(0)) were observed. Both maxima are found to be re lated to the penetration of the AC field up to the middle of a sample. This size effect occurs if the direction of the AC magnetic field differs signi ficantly from the principal axes of symmetry. Such an unusual manifestation of the size effect can be understood under the assumption that two compone nts of the AC field along the principal axes of symmetry are independently shielded by the two principal components of the anisotropic critical curren t density. The obtained results are interpreted within the framework of the critical state model generalized to the anisotropic case. (C) 2001 Elsevie r Science B.V. All rights reserved.