Rhombic skyrmion lattice coupled with orthorhombic structural distortion in EuAl$_{4}$

TL;DR

This study uncovers how EuAl$_{4}$ exhibits rhombic and square skyrmion-lattice phases with associated orthorhombic distortions, highlighting the coupling between magnetic textures and lattice deformation.

Contribution

It provides the first detailed investigation of the structural distortions linked to skyrmion phases in EuAl$_{4}$ using advanced dilatometry and x-ray scattering techniques.

Findings

Rhombic SkL phase has ~0.10% orthorhombic distortion.

Square SkL phase has ~0.03% orthorhombic distortion.

Coupling between spin system and lattice deformation influences phase stability.

Abstract

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 multi-axis dilatometric investigation of EuAl$_{4}$ by means of a newly designed fiber-Bragg-grating technique complemented by a resonant x-ray scattering experiment, 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.