Incommensurate magnetic orders and topological Hall effect in the square-net centrosymmetric EuGa$_2$Al$_2$ system

TL;DR

This study uncovers multiple incommensurate magnetic states and a topological Hall effect in EuGa$_2$Al$_2$, revealing complex magnetic phases and a potential route to non-collinear spin textures driven by charge density waves.

Contribution

The paper reports the discovery of incommensurate magnetic orders and a topological Hall effect in EuGa$_2$Al$_2$, linking out-of-plane charge density waves to in-plane non-collinear spin textures.

Findings

Multiple incommensurate magnetic states identified

Topological Hall effect observed in applied magnetic field

Charge density wave coexists with magnetic order

Abstract

Neutron diffraction on the centrosymmetric square-net magnet EuGa$_2$Al$_2$ reveals multiple incommensurate magnetic states (AFM1,2,3) in zero field. In applied field, a new magnetic phase (A) is identified from magnetization and transport measurements, bounded by two of the $\mu_0H$~=~0 incommensurate magnetic phases (AFM1,helical and AFM3, cycloidal) with different moment orientations. Moreover, magneto-transport measurements indicate the presence of a topological Hall effect, with maximum values centered in the A phase. Together, these results render EuGa$_2$Al$_2$ a material with non-coplanar or topological spin texture in applied field. X-ray diffraction reveals an out-of-plane (OOP) charge density wave (CDW) below $T_{CDW} \sim$ 50 K while the magnetic propagation vector lies in plane below $T_N$ = 19.5 K. Together these data point to a new route to realizing in-plane non-collinear spin textures through an OOP CDW. In turn, these non-collinear spin textures may be unstable against the formation of topological spin textures in an applied field.