ANISOTROPY OF THE MAGNETIZATION OF SINGLE-CRYSTALS AND BULK HIGH-T(C)SUPERCONDUCTORS

Measurements of the angular dependence of the zero-field-cooled (ZFC), field-cooled (FC) and remanent magnetization of both high-T(c) single crystals and polycrystalline samples show significant anisotropy. Com parison of the results obtained on both, prove that most anisotropy is governed by the shape of the sample via the demagnetizing factors. Fo r ceramic samples, there is competition between the demagnetizing fact ors of the sample as a whole, N, and that of the grains, n. According to a suggested phenomenological model, the magnetic moment is related to the external field by a relation involving an effective demagnetizi ng factor, N(eff), which depends on the fraction of superconducting vo lume, which is itself a field dependent quantity. At low fields, N(eff ) approaches N and n for highly compact and dilute samples, respective ly. Between these extremes, N(eff) is a weighted average of N and n.