The centrosymmetric tetragonal itinerant magnet EuAl$_{4}$ exhibits an intricate magnetic phase diagram including rhombic and square skyrmion-lattice (SkL) phases in the external magnetic field. Here, we report a dilatometric investigation on EuAl$_{4}$ for three principal axes by means of the fiber-Bragg-grating technique, revealing anisotropic magnetostriction and magnetovolume effect associated with successive phase transitions. The rhombic and square SkL phases are found to possess $\sim$0.10$\%$ and $\sim$0.03$\%$ orthorhombic structural distortion within the $ab$ plane, respectively. We propose that the coupling between the spin system and the lattice deformation should be essential for the structural instability in EuAl$_{4}$, yielding a rich variety of topological spin textures with spontaneous rotational-symmetry breaking as well as a potential controllability of the SkL phases by uniaxial stress or pressure.

中文翻译：

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EuAl$_{4}$中的菱形skyrmion晶格与正交结构畸变相结合

中心对称四方流动磁体 EuAl$_{4}$ 在外部磁场中表现出复杂的磁相图，包括菱形和方形斯格明晶格 (SkL) 相。在这里，我们通过光纤布拉格光栅技术报告了对 EuAl$_{4}$ 三个主轴的膨胀测量研究，揭示了与连续相变相关的各向异性磁致伸缩和磁体积效应。发现菱形和方形 SkL 相在 $ab$ 平面内分别具有 $\sim$0.10$\%$ 和 $\sim$0.03$\%$ 正交结构畸变。我们建议自旋系统和晶格变形之间的耦合对于 EuAl$_{4}$ 的结构不稳定性应该是必不可少的，