Observation of Topological Chirality Switching Induced Freezing of a Skyrmion Crystal

TL;DR

Researchers observed how magnetic skyrmions in CrBr3 can switch chirality under a magnetic field, leading to a freezing of their lattice structure, which could enable new spintronic devices.

Contribution

Demonstration of chirality switching-induced freezing in skyrmion lattices using in-plane magnetic fields in CrBr3.

Findings

In-plane magnetic fields enable spontaneous chirality fluctuations in skyrmionic bubbles.

Chirality switching causes elongation and shrinkage of bubbles, leading to lattice crystallization.

The process transitions the skyrmion lattice from a disordered liquid to a hexatic phase resembling a solid.

Abstract

Magnetic skyrmions are topologically protected quasi‐particles with a well‐defined chirality. Control over their chirality is proposed as an additional feature for encoding data bits or as qubits in quantum computing due to their high efficiency and stability against achiral magnetic textures. Here it is shown that an in‐plane magnetic field can be utilized to reshape the energy barriers between different skyrmionic bubbles (e.g., Bloch type, type‐II) enabling spontaneous chirality fluctuations with a frequency that increases with the strength of the in‐plane field. The insulating van der Waals ferromagnet CrBr3 is used as an archetypal system for low damping, reduced energy dissipation and a high number of magnetic phases to capture the chirality dynamics in real time through cryo‐Lorentz transmission electron microscopy. It is observed that the interplay between the intrinsic Dzyaloshinskii–Moriya interaction and out‐of‐plane field biased the chirality dynamics, favoring one handedness over the other. A remarkable consequence of the spontaneous chirality switching mechanism is that it induces a freezing (or crystallization) process in the skyrmion lattice. As the bubbles fluctuate between Bloch and type‐II they elongate and shrink parallel to the in‐plane field. Subsequently, the overall lattice crystallizes along the in‐plane field direction, inducing a phase transition from a disordered liquid state to a hexatic phase where skyrmions are highly ordered resembling that of a solid. The results indicate chirality as an active element in the creation of topologically protected skyrmion crystals unveiling pathways toward chiral spintronic device platforms with tunable embedded configuration.

Using Lorentz Transmission electron microscopy, it is shown that in the insulating van der Waals ferromagnet, CrBr3, a magnetic field can cause Bloch skyrmionic bubbles to spontaneously switch their chirality. As achiral type‐II bubbles are an intermediate state, the bubbles rapidly elongate and shrink when switching, thereby inducing a freezing of the overall bubble lattice. The control over skyrmion chirality and order shown here can allow the creation of designer skyrmion crystals for utilization in unconventional computing.

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