Correlation between Complex Spin Textures and the Magnetocaloric and Hall Effects in Eu(Ga$_{1-x}$Al$_x$)$_4$ ($x$ = 0.9, 1)

TL;DR

This study explores the relationship between complex spin textures, magnetocaloric effects, and Hall effects in Eu(Ga$_{1-x}$Al$_x$)$_4$, revealing that maximal Hall effects are linked to frustrated spin fluctuations rather than skyrmion lattice phases.

Contribution

It demonstrates that the maximal topological Hall effect in Eu(Ga$_{1-x}$Al$_x$)$_4$ does not coincide with skyrmion lattice phases but is better associated with magnetocaloric effect boundaries.

Findings

Maximal THE does not align with skyrmion lattice regions.

Magnetocaloric effect boundaries better identify skyrmion lattice phases.

Maximal THE arises from interactions with frustrated spin fluctuations.

Abstract

Determining the electronic phase diagram of a quantum material as a function of temperature (T) and applied magnetic field (H) forms the basis for understanding the microscopic origin of transport properties, such as the anomalous Hall effect (AHE) and topological Hall effect (THE). For many magnetic quantum materials, including EuAl$_4$, a THE arises from a topologically protected magnetic skyrmion lattice with a non-zero scalar spin chirality. We identified a square skyrmion lattice (sSkL) peak in Eu(Ga$_{1-x}$Al$_x$)$_4$ ($x$ = 0.9) identical to the peak previously observed in EuAl$_4$ by performing neutron scattering measurements throughout the phase diagram. Comparing these neutron results with transport measurements, we found that in both compounds the maximal THE does not correspond to the sSkL area. Instead of the maximal THE, the maximal magnetocaloric effect (MCE) boundaries better identify the sSkL lattice phase observed by neutron scattering measurements. The maximal THE therefore arises from interactions of itinerant electrons with frustrated spin fluctuations in a topologically trivial magnetic state.