MAGNETIC DOMAIN-STRUCTURES OF FERROMAGNETIC ULTRA-THIN FILMS DEPOSITED ON SUPERCONDUCTING SUBSTRATES

The influence of bulk superconducting substrates and coatings on the d omain structure parameters of a ferromagnetic ultra-thin film was anal ysed, assuming the validity of the London equation in the superconduct ing volumes. The problem was analysed for both easy plane and perpendi cular easy axis films; however, as the effects of the superconducting substrate are relatively unimportant for films magnetized in plane, mo st of the article is devoted to easy axis films. Expressions for the d emagnetization energy were found for arbitrary magnetization distribut ion. It was shown that a superconducting substrate changes the domain structure properties even if the layer is coated with a non-supercondu cting material. For sufficiently thin films the domain structure can b e fully suppressed, which was shown by considering an isolated Bloch w all for larger anisotropy (Q > 1) and the critical domain structure fo r low anisotropy (Q < 1). The results of numerical calculations for cr itical ferromagnetic film thickness (as a function of anisotropy and L ondon penetration depth) are presented.