Fluctuation-driven topological Hall effect in room-temperature itinerant helimagnet Fe3Ga4

TL;DR

This study reveals a fluctuation-driven topological Hall effect in Fe3Ga4 at room temperature, linked to chiral magnons and nontrivial magnetic phases, challenging traditional understanding of scalar spin chirality origins.

Contribution

It demonstrates a new fluctuation-driven mechanism for the topological Hall effect in a low-symmetry itinerant helimagnet, expanding the scope of materials exhibiting topological magnetic phenomena.

Findings

Room-temperature THE observed in Fe3Ga4.

Identification of nontrivial magnetic phases via neutron scattering.

The helical spiral transforms into a transverse conical state under magnetic field.

Abstract

The topological Hall effect (THE) is a hallmark of a non-trivial geometric spin arrangement in a magnetic metal, originating from a finite scalar spin chirality (SSC). The associated Berry phase is often a consequence of non-coplanar magnetic structures identified by multiple k-vectors. For single-k magnetic structures however with zero SSC, the emergence of a finite topological Hall signal presents a conceptual challenge. Here, we report that a fluctuation-driven mechanism involving chiral magnons is responsible for the observed THE in a low-symmetry compound, monoclinic Fe3Ga4. Through neutron scattering experiments, we discovered several nontrivial magnetic phases in this system. In our focus is the helical spiral phase at room temperature, which transforms into a transverse conical state in applied magnetic field, supporting a significant THE signal up to and above room temperature. Our work offers a fresh perspective in the search for novel materials with intertwined topological magnetic and transport properties.