Features of flat superconductors magnetization in perpendicular field

Magnetic flux behavior in flat type II superconductors in external perpendicular field has some peculiarities determined only by their shape. The most important one is a barrier-like initial flux penetration into such thin samples with rectangular cross-sections. Another one is a rather peculiar flux penetration pattern if the sample is not a circular disk. These features, showing inapplicability of the ellipsoidal approximation to real samples, are demonstrated by means of direct magneto-optical observations. (orig.)