Periodic vortex and current structures in superconductor-ferromagnet bilayer

Abstract

The formation of a periodic vortex and current structures in the ferromagnet/superconductor bilayer with finite interlayer distance a is considered when the ferromagnetic film has a stripe domain structure with out-of-plane magnetization. The integrodifferential equation which determines the current and vortex distribution in the superconducting (SC) film is derived. The analytical solutions are obtained for two limiting cases: L<λ (the narrow-domain structure) and L⪢λ (the wide-domain structure), where L is the width of the domain and λ=λL2ds is the effective penetration depth (where λL is the London penetration depth and ds is the thickness of the SC film). The conditions for existence of two periodic vortex structures in the SC are found (i) for the chains of vortices/antivortices (one vortex/antivortex per domain) and (ii) for the domelike vortex distribution characterized by the average vortex density n(x). The value of the critical current (along the domains) of the superconducting film is calculated. It is shown that there is the optimal interlayer distance a∗ corresponding to the maximal value of the critical current at a given value of the magnetization.

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