In-plane Antiferromagnetism in Ferromagnetic Kagome Semimetal Co3Sn2S2

TL;DR

This study reveals an in-plane antiferromagnetic phase coexisting with ferromagnetism in Co3Sn2S2, a Weyl semimetal, using advanced spectroscopic techniques, highlighting complex magnetic inhomogeneity affecting its electronic properties.

Contribution

It provides direct evidence of an in-plane antiferromagnetic phase in Co3Sn2S2 and explores its coexistence with ferromagnetism, advancing understanding of its magnetic structure.

Findings

Detection of in-plane AFM phase via {b5}-ARPES and DFT

Identification of a surface flat band at the Fermi level

AFM phase persists down to 6 K

Abstract

Co3Sn2S2 has been reported to be a Weyl semimetal with broken time-reversal symmetry with c axis ferromagnetism (FM) below a Curie temperature of 177 K. Despite the large interest in Co3Sn2S2, the magnetic structure is still under debate and recent studies have challenged our understanding of the magnetic phase diagram of Co3Sn2S2 by reporting unusual magnetic phases including the presence of exchange bias. Understanding the magnetism of Co3Sn2S2 is important since its electronic band structure including the much-celebrated flat bands and Weyl nodes depend on the magnetic phase. In this work, using X-ray Magnetic Circular Dichroism (XMCD), we establish that the magnetic moment in Co arises from the spin, with negligible orbital moment. In addition, we detect an in-plane AFM minority phase in the sea of a FM phase using spatially-resolved angle-resolved photoemission spectroscopy ({\mu}-ARPES) combined with density functional theory (DFT) calculation. Separately, we detect a sharp flat band precisely at the Fermi level (EF) at some regions in the sample, which we attribute to a surface state. The AFM phase survives even to the low temperature of 6 K. This example of entirely different magnetic ground states in a stoichiometric intermetallic invites further efforts to explore the observed AFM phase and understand the origin and nature of the magnetic and electronic inhomogeneity on the mesoscale and the interface between the AFM and FM phases.