Magneto‐optical observation of flux pinning at the grain boundary in a Bi2Sr2CaCu2Ox superconductor

Magnetic flux density distributions in a Bi2Sr2CaCu2Ox superconducting crystal for fields perpendicular to the bc plane are observed by a magneto‐optical technique. It is recognized that flux is pinned at the low angle grain boundary while barely pinned at the high angle boundary or in the intragranular regions. The contributions of the low angle boundary to the critical current density and the magnetization are estimated from the magneto‐optical results by using a flux pinning model, and then compared with the results of magnetization measurements.