Interaction of mesoscopic magnetic textures with superconductors

Abstract

We analyze magnetic textures in a thin magnetic film and screening currents induced by these textures in a superconducting film. The two films are supposed to be parallel and close each to other, but interact only via magnetic fields. We consider also vortices inside superconducting film and their interaction with magnetic textures. As examples of magnetic textures we consider magnetic dot and magnetic vortex. We derive the condition at which spontaneous formation of a vortex or a coupled vortex-magnetic defect is energetically favorable. It is proven that the normal component of magnetic field generated by a magnetic dot changes sign in the presence of the superconducting vortex.74.60. Ge, 74.25.Ha, 74.25.Dw The fabrication and experimental study [1] of mesoscopic heterogeneous magnetic/superconducting systems together with recent theoretical predictions [2][3][4] open a new class of physical effects. Earlier two of us (I.F.L. and V.L.P.) proposed to separate superconductivity and magnetism in space employing the modern technique of nanofabrication [2]. The proximity effect which suppresses both order parameters can be easily avoided by growing insulator oxide layers between ferromagnetic (FM) and superconducting (SC) components. Inhomogeneous magnetization of the magnetic texture generates magnetic field penetrating into the superconductor. The magnetic field from the SC currents interacts with magnetic subsystem [3,4]. We have proposed different realizations of mesoscopic magneto-superconducting systems: arrays of magnetic dots on the top of a superconducting film [2], magnetic/superconducting bi-layers [3], magnetic nanorods embedded into a superconductor [4].In the majority of proposed systems a magnetic texture interacts with the superconducting current. An inhomogeneous magnetization generates magnetic field outside the magnet. The magnetic field generates screening currents in superconductors which, in turn, change the magnetic field. The problem must be solved self-consistently . In this article we develop a general formalism for interacting inhomogeneous magnetization (texture) and superconductors in the London's approximation. Employing this formalism, we find two elementary solutions for a circular magnetic dot on the top of a superconducting film, magnetized perpendicularly to it, and for a coupled magnetic and superconducting vortices. London's approximation works satisfactory since the sizes of all structures in the problem exceeds remarkably the coherence length ξ.Recent theoretical works [5][6][7] consider problems close to ours. The main difference between our work and the Ref.[6] is that they do not incorporate spontaneous vortices in the ground state. In comparison to the Refs. [5,7] our approach is more general and universal. A more detailed comparison with these references will be given later.So far only arrays of sub-micron size magnetic dots covered by thin superconducting films have been prepared and studied experimentally [1] * * . The effect of commencuracy on the transport properti...

Erratum: Interaction between superconducting films and magnetic nanostructures [Phys. Rev. B66, 104508 (2002)]

“…Recently, the development of magnetic thin film technology has triggered a lot of interest in this field. Of particular importance has been the possibility of examining the interaction between superconductivity and magnetism in high-temperature superconductors [6][7][8][9][10][11][12][13][14][15].…”

London study of vortex states in a superconducting film due to a magnetic dot

“…1). The dot's magnetization reads The energy of the system in the presence of many vortices with arbitrary vorticities n i is described elsewhere [19]. The appearance of N vortices with arbitrary positions r i in the system changes the energy by an amount:…”

“…Earlier, we studied the vortex states due to a ferromagnetic (FM) dot with out-of-plane ( perpendicular to the film ) magnetization on top of a SC thin film [19]. In that work, we limited ourselves only to the vortices trapped under the dot, and calculated the equilibrium configurations, up to three vortices.…”

“…al. recently reported the experimental evidence of the GV states and the other rearrangements of vortices in a mesoscopic SC disc, using the multiple-tunnel-junction method [17].Earlier, we studied the vortex states due to a ferromagnetic (FM) dot with out-of-plane ( perpendicular to the film ) magnetization on top of a SC thin film [19]. In that work, we limited ourselves only to the vortices trapped under the dot, and calculated the equilibrium configurations, up to three vortices.…”

“…For this purpose, we pursue the method based on London-Maxwell equations, which is fully developed elsewhere [19]. Though the London approach works well at the high κ = Λ/ξ limit, it perfectly serves our purpose and enables us to do analytical calculations.…”