Demagnetizing fields of crystallites and a method for measuring the thermodynamic fields of quasi-single-crystal and polycrystalline thin YBa2Cu3O7 − x disks

The role of the demagnetizing fields of crystallites in HTSC samples is studied. An increase in the crystallite size is shown to suppress the intra-and intercrystalline critical currents of the sample in lower fields. The demagnetizing fields of crystallites are shown to be one of the main causes of the fact that the Bean model is invalid for HTSC samples. A method is proposed to measure the thermodynamic field of a superconductor; this method allows the first thermodynamic critical magnetic fields of the sample and its crystallites and “subcrystallites” to be measured with a high accuracy. The first thermodynamic critical magnetic fields are used to estimate the critical current density Jc of the sample, crystallites, and subcrystallites.