Temperature and Dimensional Dependence of the Irreversibility Field of a Layered High-Temperature Superconductor

The Monte Carlo method was used in a 2D model of the layered HTSC to calculate the magnetization curves of a granulated high-temperature superconductor for various sizes of granules. In this approach magnetization of granules alone is taken into account, while the contribution of the gaps between granules is small and neglected. The irreversibility field has been found to decrease with temperature at the fixed size of granules and increase as the granule size increases at fixed temperature. The time dependence of residual magnetization has been studied at various temperatures. The relaxation rate is shown not to depend on the granule size at low temperatures but to decrease with the increasing size (provided that the granule size is less than 3 μm) at a high temperature when the magnetic flux creep becomes of importance.