The remanent and in-field magnetic field distributions of 2 crystals, one with a single twin boundary and one completely untwinned, were observed by using a non-destructive magneto-optical technique. Geometrical barrier effects upon the flux penetration of both samples were found. Two distinct penetrating field patterns were observed, which resulted from the differing pinning characteristics of the samples. A concentration of penetrating vortices in the center of one sample indicated an extremely low degree of pinning. A comparison was made between the observed flux penetration profiles of both samples, and those calculated by using a theoretical model for a thin strip superconductor. A single twin boundary in the extremely low-pinning crystal was observed to be a barrier to transverse vortex motion.

M.W.Gardner, S.A.Govorkov, R.Liang, D.A.Bonn, J.F.Carolan, W.N.Hardy: Journal of Applied Physics, 1998, 83[7], 3714-9