Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet

Abstract: Geometrically frustrated magnets provide abundant opportunities for discovering complex spin textures, which sometimes yield unconventional electromagnetic responses in correlated electron systems. It is theoretically predicted that magnetic frustration may also promote a topologically nontrivial spin state, i.e., magnetic skyrmions, which are nanometric spin vortices. Empirically, however, skyrmions are essentially concomitant with noncentrosymmetric lattice structures or interfacial-symmetry-breaking heterostructures. Here, we report the emergence of a Bloch-type skyrmion state in the frustrated centrosymmetric triangular-lattice magnet Gd2PdSi3. We identified the field-induced skyrmion phase via a giant topological Hall response, which is further corroborated by the observation of in-plane spin modulation probed by resonant x-ray scattering. Our results exemplify a new gold mine of magnetic frustration for producing topological spin textures endowed with emergent electrodynamics in centrosymmetric magnets.

• The paper identifies a Bloch-type skyrmion lattice in the frustrated triangular magnet Gd2PdSi3.
• It employs resonant X-ray scattering to reveal a triple-Q multi-helical spin modulation structure.
• The study reports a topological Hall resistivity of 2.6 μΩcm, indicating promising spintronic applications.

Insights into Skyrmion Lattice and Topological Hall Effect in Gd$_2$PdSi$_3$

In the presented study, researchers investigated the emergence of a skyrmion lattice (SkL) state in the geometrically frustrated metallic magnet Gd$_2$PdSi$_3$. The study reveals a novel magnetic configuration that manifests as a Bloch-type skyrmion state under an applied magnetic field. This paper presents compelling evidence of this phase transition through the observation of a significant topological Hall effect (THE), an attribute associated with skyrmion dynamics.

Emergence of Skyrmions in Centrosymmetric Lattices

Skyrmions, topologically stable vortex-like spin textures, have mostly been observed in noncentrosymmetric systems where Dzyaloshinskii-Moriya (DM) interactions stabilize these configurations. However, this paper reports the stabilization of skyrmion lattices in a centrosymmetric lattice, namely, the triangular lattice network of Gd atoms in Gd$_2$PdSi$_3$. The absence of DM interactions implies a stabilization mechanism based on frustrated magnetic interactions, specifically through the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.

Topological Hall Effect as a Diagnostic Tool

The topological Hall effect, characterized by an emergent magnetic field due to the nontrivial topology of skyrmion lattices, serves as an indicator of skyrmion presence. The researchers observed a topological Hall resistivity as large as 2.6 μΩcm at low temperatures in the SkL phase of Gd$_2$PdSi$_3$. This value is substantially higher compared to other skyrmion-hosting materials, suggesting a strong coupling and a more pronounced skyrmion configuration.

Resonant X-ray Scattering and Magnetic Structures

Resonant X-ray scattering (RXS) techniques were employed to explore the spin modulations in the SkL phase. The study identifies a long-range Gd spin modulation in the triangular lattice plane, confirming the formation of the Bloch-type skyrmion state. Furthermore, the observed modulations fit a triple-Q model with a unique multi-helical structure, deviating from typical single-Q helical states found in skyrmion systems with noncentrosymmetric structures.

Theoretical and Practical Implications

The results challenge the conventional understanding that noncentrosymmetry is a prerequisite for skyrmion formation. The realization of skyrmions in a centrosymmetric lattice broadens the scope of materials that can host these topological features. The insight opens new research directions in the design of materials with emergent topological properties without relying on inherent crystal structure symmetries.

Furthermore, the high magnitude of the topological Hall resistivity highlights the potential application of such systems in spintronic devices. The study's insights into the effects of magnetic frustration on spin textures may drive innovative approaches to control skyrmion dynamics in applied fields.

Future Perspectives

The study of frustrated magnetic systems such as Gd$_2$PdSi$_3$ deepens the understanding of topological spin textures and their electrodynamic responses. Future research could focus on exploring similar phenomena in other frustrated lattices or materials, expanding the fundamental understanding of magnetic skyrmions in various geometrical and interaction contexts. Further theoretical models could also explore the coupling strengths and energy scales pertinent to the stabilization of these complex spin structures.

Overall, this research offers novel insights into the physics of skyrmion lattices and motivates further exploration of frustrated magnetic systems as platforms for topological phenomena.