Nucleation of superconductivity in an Al mesoscopic disk with magnetic dot

Abstract

We have studied the nucleation of superconductivity in a mesoscopic Al disk with a Co/Pd magnetic dot placed on the top by measuring the normal/superconducting phase boundary Tc(B). The measurements have revealed a pronounced asymmetry in the phase boundary with respect to the direction of the applied magnetic field, indicating an enhancement of the critical field when an applied magnetic field is oriented parallel to the magnetization of the magnetic dot. The theoretical Tc(B) curve is in a good agreement with the experimental data. PACS numbers: 74.78.Na, 74.25.Dw,

Multiquanta Vortex Entry and Vortex-Antivortex Pattern Expansion in a Superconducting Microsquare with a Magnetic Dot

“…Figure 1 shows, together with a schematic drawing of the superconducting square with the magnetic dot on top, the field profile that was obtained from Eq. (3) by using M dot 18 0 , R 0:4a, l 0:033a, and z ÿ0:0025a (here a is the square's length), parameters that are comparable with those of dots previously used in experiments [6,8]. The details of the gauge transformation of Eq.…”

“…In the case of individual nanostructures, these studies have been focused on a cylindrical symmetry of the superconductor, but they have already revealed new physical phenomena arising from the interaction between superconductivity and magnetism at this submicrometer scale. A good example is the profound influence that a magnetic dot may have on the onset of superconductivity and vortex states in loops and disks [5,6].In this Letter, we investigate the nucleation of superconductivity in a square with a cylindrical magnetic dot on top. The existing analytic procedure to solve the linearized Ginzburg-Landau equation (LGLE) in regular polygons [7] has been adapted to include the contribution of the dot to the total magnetic field, allowing us to identify new quantum effects in the onset of superconductivity arising from the interplay between the finite rotational symmetry of the square and the inhomogeneous field of the dot.…”

“…For instance, in cylindrical geometries, the superconductivity nucleates in the form of a giant vortex in the center [2], while symmetry-consistent vortexantivortex patterns may be spontaneously created in both triangles [3] and squares [4]. This interest in the confinement effects has been recently extended to hybrid superconductor/ferromagnetic (SF) nanosystems [5,6]. In the case of individual nanostructures, these studies have been focused on a cylindrical symmetry of the superconductor, but they have already revealed new physical phenomena arising from the interaction between superconductivity and magnetism at this submicrometer scale.…”

“…The existing analytic procedure to solve the linearized Ginzburg-Landau equation (LGLE) in regular polygons [7] has been adapted to include the contribution of the dot to the total magnetic field, allowing us to identify new quantum effects in the onset of superconductivity arising from the interplay between the finite rotational symmetry of the square and the inhomogeneous field of the dot. These effects, which include vorticity changes by more than 1 associated with multiquanta vortex entries in the sample and an expansion of the symmetry-consistent vortexantivortex patterns, are well beyond those expected for a cylindrical geometry of the superconductor [5,6,8].The most adequate tool to study the nucleation of superconductivity is the LGLE given by [9] ÿir ÿ 2 0Equation (1) is analogous to the Schrödinger equation [10]. So, as the latter, it will preserve in the solutions the symmetry imposed by the boundary conditions, which in the case of a superconductor-vacuum interface can be written as…”

“…In the case of individual nanostructures, these studies have been focused on a cylindrical symmetry of the superconductor, but they have already revealed new physical phenomena arising from the interaction between superconductivity and magnetism at this submicrometer scale. A good example is the profound influence that a magnetic dot may have on the onset of superconductivity and vortex states in loops and disks [5,6].…”