Finite size effects on magnetic flux penetration into YBCO/LSMO hybrids

The attractive idea to create artificial superconductor/ferromagnet heterostructures (SC/FM) for easy control of the superconductor properties by magnetic field is widely considered last decade. Of a special interest for applications are the HTSC/FM heterostructures, particularly the YBCO/LSMO, where the magnetization value of LSMO could be adjusted by doping, by variation of oxygen content, and magnetic domain structure could be controlled by reasonable magnetic field. We concentrate on the in-plane field penetration into the YBCO/LSMO hybrid film, which is of practical interest as the in-plane field easier saturates the magnetic film. The study is performed by the magneto-optic visualization technique at T down to 7 K. We found a striking transformation of the in-plane external field into a wave of alternating perpendicular flux, the particular features of which depended on the temperature and magnetic prehistory at temperature above superconducting transition. To shed light on the mechanism of the effect, we have investigated the magnetic domain pattern of manganite film and it's transformations due to variation of temperature and the field. The results are discussed taking into account the finite size of the hybrid structure and the magnetostatic field distribution.