Bloch Point Quadrupole Constituting Hybrid Topological Strings Revealed with Electron Holographic Vector Field...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Topological magnetic (anti)skyrmions are 2D string-like objects with potential in spintronics.
• Intrinsically 3D electron-spin topology in magnets is less explored than 2D counterparts.
• Previous 2D imaging suggested complex 3D structures in antiskyrmion-hosting magnets.

Purpose of the Study:

• To investigate the 3D real-space structure of antiskyrmions.
• To explore the topological nature of spin textures in (Fe0.63Ni0.3Pd0.07)3P (FNPP) lamellae.
• To understand the stability and properties of these 3D spin structures.

Main Methods:

• Holographic vector field electron tomography was used to capture 3D antiskyrmion structures.
• Experiments were conducted on single-crystal, precision-doped FNPP lamellae at room temperature and zero field.
• Numerical calculations were performed to corroborate the stability of observed structures.

Main Results:

• 3D antiskyrmions were revealed as hybrid string-like solitons, with W = -1 skyrmions on surfaces and a W = +1 antiskyrmion connecting them.
• A Bloch point quadrupole, undetectable in 2D imaging, was discovered, enabling topological transitions.
• Hybrid strings demonstrated greater stability than conventional (anti)skyrmions.

Conclusions:

• The 3D structure of antiskyrmions is a hybrid string, challenging 2D models.
• These hybrid strings enable topological tuning and a tunable topological Hall effect.
• The findings disrupt existing spintronics paradigms by suppressing skyrmion Hall motion.