Experimental demonstration of shrinkage of magnetic domains in a superconductor/ferromagnet bilayer

The shrinkage of magnetic domains in a superconductor/ferromagnet bilayer is studied experimentally using Pb as a superconductor and a garnet film with maze domains as a ferromagnet. The effects of trapped flux in a superconductor and the pinning of magnetic domain boundaries are carefully minimized by using a high-quality Pb single crystal and an AC demagnetization technique. A temperature independent shrinkage of magnetic domains by a factor ∼ 0.89 is obtained below the superconducting transition of Pb. The slightly suppressed shrinkage ratio as compared with the theoretical prediction can be explained by a finite gap between the Pb crystal and the garnet film.