New electronic phase in kagome ferromagnet Co3Sn2S2 probed by spatially resolved ARPES

Shandite Co₃Sn₂S₂ has been synthesized and studied extensively, but there is still a lack of consensus regarding the magnetic ground state. Since its discovery, it has been considered a ferromagnet with c-axis as its easy axis. However, recently, there has been reports of exchange bias based on magnetometry and anomalous Hall effect attributed to spin glass and presence of antiferromagnetism at magnetic domains walls. Separately, muon spin rotation has reported an antiferromagnetic phase coexisting with a ferromagnetic phase. On the other hand, neutron scattering and non-linear optics experiments in Co₃Sn₂S₂ have not detected phase separation between antiferromagnetic and ferromagnetic phases and instead suggest a homogenous c-axis ferromagnetic phase or a canted c-axis ferromagnetic phase, respectively. Conventional local probe techniques such as Magnetic Force Microscopy (MFM) and Magneto Optic Kerr Effect (MOKE) have not detected any antiferromagnetic phase either.



We employ an indirect local probe to investigate the magnetic phase of Co₃Sn₂S₂: spatially resolved Angular Resolved Photoemission Spectroscopy (ARPES) combined with Density Functional Theory (DFT) calculations. Based on DFT calculations, the band structure of Co₃Sn₂S₂ is significantly different in the ferromagnetic vs antiferromagnetic phase. By spatially mapping the local band structure, we discover small regions of the sample that match the antiferromagnetic band structure rather than the ferromagnetic band structure at 6 K. This band converts to a band corresponding to the paramagnetic phase at 200 K, indicating that it is coupled to the magnetic phase. In addition, we detect a much sought sharp flat band at the Fermi level in selected regions of the sample, which we attribute to a surface state.