Magnetic structure of superconductor/ferromagnet bilayer

Changes in the magnetic domain structure in Pb/Bi-substituted iron–garnet bilayer have been studied using magneto-optical imaging. It is found that the theoretically predicted shrinkage of the magnetic domain below the superconducting transition temperature of Pb is not observed. We speculate that the strong pinning of the magnetic domains in the garnet film prevents the magnetic domains attaining the equilibrium configuration. We have also attempted to detect possible domain-wall superconductivity in Pb/BaFe12O19 bilayer system. No clear signs of either the domain-wall superconductivity nor the reversed-domain superconductivity have been observed. Instead, discontinuous and inhomogeneous changes of magnetic domains are observed below about 15 K.