Speaker
Description
Antiferromagnets have long been regarded as magnetically compensated systems that lack the spontaneous electromagnetic responses characteristic of ferromagnets. However, recent advances in both experiment and theory have revealed that antiferromagnetic order can host a rich variety of electromagnetic phenomena when combined with symmetry breaking and complex spin textures. In this talk, we will present our recent studies to uncover emergent electromagnetic responses arising from antiferromagnetism with broken time-reversal symmetry.
In the first part, we will present our recent findings that rare-earth-based intermetallics with centrosymmetric tetragonal crystal structures can host nanoscale magnetic skyrmion lattices, exhibiting relatively large topological Hall effects. Our target material system features a layered crystal structure, where conducting layers alternate with magnetic rare-earth layers, resulting in strong coupling between conduction electrons and localized moments. Due to their centrosymmetric crystal structures, itinerant-electron-mediated magnetic interactions are expected to play a crucial role in the formation of nanoscale skyrmions. GdRu2Si2 hosts a square skyrmion lattice, while GdRu2Ge2 and EuAl4 exhibit square and rhombic lattices of skyrmions with multiple-step topological magnetic phase transitions. These features suggest that the symmetry of the skyrmion lattice is sensitive to the electronic structure and can be controlled through chemical substitution and external stimuli.
In the second part, we present our experimental observation of a spontaneous Hall effect in the collinear antiferromagnet FeS at room temperature. FeS hosts antiferromagnetically ordered Fe moments together with a staggered arrangement of non-magnetic S ions, giving rise to an altermagnetic electronic structure. Our analysis indicates that the spontaneous Hall effect originates from a momentum-dependent fictitious magnetic field intrinsic to the antiferromagnetic order lacking time-reversal symmetry.
Together, these results demonstrate that antiferromagnets can host a wide variety of unconventional electromagnetic responses and may lead to functionalities beyond the traditional ferromagnetic paradigm.
| Field of Condensed Matter | Magnetism |
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