Topological textures in a ferromagnet-superconductor bilayer.

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Ferromagnet-superconductor bilayers (FSBs) can exhibit complex behaviors due to the interplay between magnetic and superconducting properties.
• A homogeneous magnetic state, particularly with magnetization perpendicular to the layer, can be susceptible to instabilities.

Purpose of the Study:

• To investigate the topological instability in ferromagnet-superconductor bilayers.
• To understand the formation of novel combined topological structures involving magnetization and vorticity.

Main Methods:

• Theoretical analysis of the ferromagnet-superconductor bilayer system.
• Investigation of the stability of the homogeneous magnetic state.
• Characterization of the emergent domain structures.

Main Results:

• The homogeneous state of an FSB with perpendicular magnetization is unstable, leading to vortex formation in the superconductor.
• A topological instability drives the formation of alternating domains of magnetization and vorticity.
• This combined topological structure is unique to the bilayer system and not observed in isolated layers.
• Equilibrium domains can form even when the magnetic layer is in a monodomain state.

Conclusions:

• Ferromagnet-superconductor bilayers host a novel combined topological structure arising from magnetic-superconducting interactions.
• This instability provides a new mechanism for creating complex magnetic and vorticity patterns in layered materials.