Vortex observations in the triangular microhole lattice on Pb film by SQUID microscope

We have investigated the magnetic properties of a triangular microhole lattice on Pb film (TriMHoLP) by means of a SQUID magnetometer and a SQUID microscope. A matching field H of TriMHoLP is 0.425 G. The zero-field-cooled magnetization curves are in accordance with those expected for typical superconductors. However, the curves observed in a field-cooled mode upon cooling are always negative and irrelevant to the field polarity at temperatures just below Tc. Even in the zero field, we have observed both positive and negative field modulation by the SQUID microscope. The field modulation coincides well with the microhole structure. These strongly suggest that there must be a spontaneous magnetization in TriMHoLP at temperatures near Tc. We also give a vector map of the current density reproduced from a local field distribution.