Crossover between different regimes of inhomogeneous superconductivity in planar superconductor-ferromagnet hybrids

TL;DR

This study experimentally investigates how a stripe-like ferromagnetic domain structure influences inhomogeneous superconductivity in a superconductor-ferromagnet hybrid, revealing regimes of reverse-domain and edge-assisted superconductivity controlled by magnetic fields.

Contribution

It demonstrates the formation and control of inhomogeneous superconducting states in superconductor-ferromagnet hybrids, including reverse-domain and edge-assisted regimes, using magnetic field ratios and microscopy.

Findings

Identification of reverse-domain superconductivity regimes

Observation of edge-assisted localized superconductivity

External magnetic field controls inhomogeneous superconducting states

Abstract

We studied experimentally the effect of a stripe-like domain structure in a ferromagnetic BaFe_{12}O_{19} substrate on the magnetoresistance of a superconducting Pb microbridge. The system was designed in such a way that the bridge is oriented perpendicular to the domain walls. It is demonstrated that depending on the ratio between the amplitude of the nonuniform magnetic field B_0, induced by the ferromagnet, and the upper critical field H_{c2} of the superconducting material, the regions of the reverse-domain superconductivity in the H-T plane can be isolated or can overlap (H is the external magnetic field, T is temperature). The latter case corresponds to the condition B_0/H_{c2}<1 and results in the formation of superconductivity above the magnetic domains of both polarities. We discovered the regime of edge-assisted reverse-domain superconductivity, corresponding to localized superconductivity near the edges of the bridge above the compensated magnetic domains. Direct verification of the formation of inhomogeneous superconducting states and external-field-controlled switching between normal state and inhomogeneous superconductivity were obtained by low-temperature scanning laser microscopy.