Magnetization hysteresis loops of the granular high-Tc superconductors in the AC measurements

Abstract In this paper, with some improvements to the conventional AC response technique, we report experimentally on the M - H hysteresis loops at different temperatures and frequencies when applying an AC field H = h o sin( σt ) to the granular superconductor of YBa 2 Cu 3 O 6.4 . Two kinds of hysteresis loops are found with different shapes in different AC field frequencies. Based on the simple Bean model and the extended Bean model, considering the influence of the intergranular lower critical field, we derived the expressions of the magnetization in the AC case, which are in good agreement with the M - H curves measured by our experiments.