Visualization of the vortex-mediated pinning of ferromagnetic domains in superconductor-ferromagnet hybrids

A thin superconducting (S) film reduces the mobility of magnetic domains in an underlying ferromagnet (F). The magnetic domain pattern of a barium hexaferrite single crystal was imaged as a function of temperature and external magnetic field, in both presence and absence of a covering niobium film. Comparative analysis of these two cases reveals that the relaxation of the domains is hampered, if the external field is changed while the Nb-film is superconducting. This effect in the S/F hybrids is interpreted in terms of a vortex-mediated pinning of magnetic domains by pinning centers in the superconductor.