Magneto-optical characterizations of composite superconductors

The magnetic flux dynamic in RE-Ba-Cu-O (RE = La, Nd, Sm, Eu or Gd) composi te superconductors processed by the oxygen-controlled-melt-growth (OCMG) me thod was investigated by magneto-optical (M-O) technique using an iron-garn et film with in-plane magnetization. An external magnetic field H was applied parallel to sample's c-axis (H par allel to c) up to 5000 Oe at different temperatures. The field distribution as well as the current paths were clearly visualized and correlated to the sample microstructure. The M-O images were associated with the data obtain ed by analysing the magnetization curves. Critical current densities were c alculated from magnetization hysteresis measurements. The direct and detail ed knowledge of the field behaviour provided by the M-O images allows preci se interpretation of the magnetization loops.