Critical field enhancement in hybrid superconductor/ferromagnet mesoscopic disks

Abstract

We investigated experimentally the nucleation of superconductivity in a mesoscopic hybrid structure, consisting of a thin superconducting disk covered with a ferromagnetic layer with an in-plane magnetic moment. By applying a magnetic field in the plane of the structure, the remanent magnetic state of the ferromagnet can be switched from a flux-closure state where field lines are confined inside the ferromagnet to a polarized state with nonzero stray fields at the edges. This change in the magnetic state causes a drastic modification on the superconductor/normal-state phase boundary of the hybrid sample. In the polarized state a re-entrant transition line and a strong broadening of the phase boundary are observed.

Nucleation of superconductivity and vortex matter in superconductor–ferromagnet hybrids

“…In addition, such ferromagnet induces two opposite screening currents inside the superconducting film plane (in the perpendicular direction to its magnetization), which effectively compensates the bias current, and therefore superconductivity should persist up to higher applied currents and fields. These effects have been recently studied experimentally by Schildermans et al [332] in an Al/Py hybrid disk of 1.7 µm diameter where a finite dipolar moment lying in the plane of the structure was achieved by pinning magnetic domains with the contact leads used for electrical measurements.…”