Weyl semimetals are a class of materials characterized by the presence of Weyl points where the valence and conduction bands touch linearly. Electrons near these points behave as relativistic fermions called Weyl fermions, contributing to topological magnetoelectric responses, such as the anomalous Hall effect. The concept of chiral gauge field was introduced to understand these topological effects. This fictitious gauge field describes the shifts in the Weyl points in the momentum space. Previous studies have shown that a chiral gauge field can be generated by external perturbations, such as light and lattice strain. This enables one to understand their effects, similar to ordinary electromagnetic fields appearing in Maxwell’s equations.

   In magnetic Weyl semimetals, the interplay between the magnetic ordering and the topological magnetoelectric responses is of particular interest. When spin–momentum locking is present, where the spin and momentum of Weyl fermions are parallel or antiparallel, the magnetization can be directly mapped to the chiral gauge field. This correspondence has led to the development of various magnetoelectric responses with potential spintronic functionalities. However, the spin–momentum locking structure depends on both spin–orbit coupling and spin polarization. This hinders the understanding of the topological magnetoelectric responses in realistic magnetic Weyl semimetals based on a chiral gauge field.

   This study investigated the chiral gauge field in relation to the magnetization in the Weyl ferromagnet Co₃Sn₂S₂. The electrons in Co₃Sn₂S₂ are nearly fully spin-polarized, leading to the absence of spin–momentum locking around the Weyl points. The effective model calculations in this study demonstrated that the positions of the Weyl points are significantly influenced by magnetization modulation, which can be described by the chiral gauge field. This result attributes the temporal and spatial variations in the magnetization within Co₃Sn₂S₂ to the chiral electric and magnetic fields. The calculations demonstrated that a magnetic domain wall with a width of 10 nm generates a large chiral magnetic field of 260 T, leading to topological magnetoelectric responses. One consequence is the charge pumping driven by domain wall dynamics, which is analogous to the quantum Hall effect induced by chiral electromagnetic fields. This effect results in an electric voltage up to 800 times higher than the spin motive force observed in conventional ferromagnetic metals. This makes Co₃Sn₂S₂ a promising material for detecting domain wall dynamics in spintronic devices, such as magnetic memories.

  The insights gained from this study on the chiral gauge field in magnetic Weyl semimetals are expected to stimulate further exploration of novel topological magnetoelectric responses associated with magnetic textures and dynamics.

(Written by A. Ozawa and Y. Araki on behalf of all the authors)

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