Skyrmion phase and competing magnetic orders on a breathing kagome lattice (1812.02553v2)

Abstract: Magnetic skyrmion textures are realized mainly in non-centrosymmetric, e.g. chiral or polar, magnets. Extending the field to centrosymmetric bulk materials is a rewarding challenge, where the released helicity / vorticity degree of freedom and higher skyrmion density result in intriguing new properties and enhanced functionality. We report here on the experimental observation of a skyrmion lattice (SkL) phase with large topological Hall effect and an incommensurate helical pitch as small as 2.8 nm in metallic Gd3Ru4Al12, which materializes a breathing kagom\'e lattice of Gadolinium moments. The magnetic structure of several ordered phases, including the SkL, is determined by resonant x-ray diffraction as well as small angle neutron scattering. The SkL and helical phases are also observed directly using Lorentz transmission electron microscopy. Among several competing phases, the SkL is promoted over a low-temperature transverse conical state by thermal fluctuations in an intermediate range of magnetic fields.

• The paper demonstrates the experimental realization of a skyrmion lattice phase in a centrosymmetric breathing kagome lattice, challenging conventional inversion symmetry requirements.
• It employs resonant x-ray diffraction, small-angle neutron scattering, and Lorentz TEM to reveal a nanoscale helical pitch of 2.8 nm along with a pronounced topological Hall effect.
• The study suggests that frustrated RKKY interactions and local anisotropy can stabilize skyrmions, paving the way for novel spintronic devices and advanced data storage applications.

Skyrmion Phase and Competing Magnetic Orders on a Breathing Kagomé Lattice

The paper explores the experimental realization of skyrmion lattice (SkL) phases within a breathing kagomé lattice structure, specifically focusing on Gd$_3$Ru$_4$Al$_{12}$, a centrosymmetric material. Skyrmions, notable for their topological properties and potential applications in data storage, typically manifest in non-centrosymmetric environments. However, this paper challenges that paradigm by presenting skyrmions in a centrosymmetric scenario, garnering insights into the magnetic behavior and related phenomena in such materials.

Experimental Observations and Methods

The magnetic profile of Gd$_3$Ru$_4$Al$_{12}$ was probed using several advanced techniques. These included resonant x-ray diffraction, small-angle neutron scattering, and Lorentz transmission electron microscopy (L-TEM). The skyrmion lattice phase and its neighboring phases were characterized by a topological Hall effect (THE) and an incommensurate helical pitch, noted to be as small as 2.8 nm. This nanoscale dimension is particularly significant when compared to classical chiral compounds like MnSi, which typically exhibit larger pitches.

Magnetic Phase Diagram and Topological Hall Effect

The paper describes a complex magnetic phase diagram for Gd$_3$Ru$_4$Al$_{12}$, highlighting a variety of states, including helical, transverse conical, fan-like, and skyrmion lattice phases. Among these, the identification of the SkL phase stands out due to its pronounced topological Hall effect. This effect, attributed to the nontrivial winding number of the skyrmion texture, provides pivotal evidence for the chiral nature of magnetic ordering within this phase.

Theoretical Implications and Future Prospects

The results have substantial implications for the theoretical understanding of skyrmions in centrosymmetric lattices. The skyrmion phase, once thought to necessitate broken inversion symmetry, here appears stabilized by a combination of frustrated RKKY interactions, local anisotropy, and thermal fluctuations without Dzyaloshinskii-Moriya interaction. This presents a potentially new avenue for materials science, suggesting that reduced spin-orbit coupling and symmetry can still permit the observation of topological spin textures like skyrmions, which in turn influence macroscopic properties such as electrical conductance.

Moreover, the confirmation of the SkL phase and metastable skyrmions in this paper emphasizes the role of the breathing kagomé lattice as a promising platform for future research into topological magnetic phases. It presents opportunities not only for expanding the understanding of two-dimensional magnetic systems but also for developing novel devices based on skyrmions in information technology.

Conclusion

The presented work on Gd$_3$Ru$_4$Al$_{12}$ broadens the scope of skyrmion research by establishing a compound where skyrmion phases exist without the conventional requirement of a non-centrosymmetric lattice. It opens potential new paths for the development of electronic devices centered on manipulating skyrmions and their associated properties. Future research will likely delve into a deeper exploration of these properties and the development of applications leveraging the unique attributes of skyrmions, especially in the context of data storage and transmission technologies.