Magnetic domain structures in superconductor/ferromagnet bilayer

We made a systematic study on the ferromagnetic (FM) domain width of Pb/garnet bilayer using magneto-optical imaging by changing the damping rate of ac demagnetizing field. As the damping rate is slower, FM domain width becomes thinner. Similar measurements on plain Pb film also show damping-rate-dependent inhomogeneous magnetic pattern originating from the pinning of vortices. These results imply that the shrinkage of FM domain width in the bilayer is also affected by the pinning of vortices. Quantitative evaluations of the characteristic size of patterns in the two systems suggest the presence of intrinsic shrinkage of the FM domain width in Pb/garnet bilayer, which is theoretically predicted. (C) 2010 Elsevier B.V. All rights reserved.