Incommensurate Magnetism and Reciprocal Space Topology in the Eu(Ga1–xAlx)4 System

Abstract:

The Eu(Ga_1–xAl_x)₄ system has recently gained attention from both a real- and reciprocal-space topology perspective. The Eu(Ga_1–xAl_x)₄ family of compounds crystallize in the centrosymmetric ThCr₂Si₂ structure type with several square-net motifs. The entire series of Eu(Ga_1–xAl_x)₄ can be synthesized, with x ranging from x = 0 to x = 1 [1]. The end compound EuAl₄ [Eu(Ga_1–xAl_x)₄ x = 1] has recently been shown to host several incommensurate magnetic structures in zero magnetic field while skyrmion lattices are stabilized with a magnetic field applied H II c [2]. The intermediate compound, EuGa₂Al₂ [Eu(Ga_1–xAl_x)₄ x = 0.5], has also been found to host incommensurate magnetism in zero magnetic field, while the observed topological Hall signal points to non-coplanar or topological spin textures with an applied magnetic field [3]. By contrast, the zero-field magnetic structure of the other end compound, EuGa₄ [Eu(Ga_1–xAl_x)₄ x = 0], has been determined to be a simple A-type antiferromagnet [4]. However, this compound is far from boring, being a topological Weyl-nodal ring candidate [5]. The Dzyaloshinkii-Moriya (DM) interaction, which has been deemed one key ingredient in stabilizing incommensurate magnetism in noncentrosymmic materials, is absent in centrosymmetric materials. Therefore, other possible mechanisms like geometric frustration or Fermi surface nesting can be responsible for the incommensurate magnetism. In the first part of this talk, I will discuss our recent density-functional theory and angle-resolved photoemission results showing that Fermi surface nesting, a consequence of the square-net geometry in Eu(Ga_1–xAl_x)₄, is likely responsible for the incommensurate magnetism in EuGa₂Al₂. In the second part of the talk, I will discuss novel transport properties we observe in EuGa₂Al₂ (large anomalous Hall effect) [6] and EuGa₄ (large, non-saturating magnetoresistance) [5], a result of Weyl physics, which we associate with the square-net geometry in the Eu(Ga_1–xAl_x)₄.

[1] Stavinoha et al. Phys. Rev. B 97, 195146 (2018).
[2] Takagi et al. Nature Communications 13, 1472 (2022).
[3] J. Moya et al. Phys. Rev. Mater. 6, 074201 (2022).
[4] Kawasaki et al. J. Phys. Soc. Japan 85, 114711 (2016).
[5] S. Lei et al. arXiv:2208.06407 (2022). [6] J. Moya et al. arXiv:2302.03076 (2023)

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