反強磁性体における巨大な磁気光学効果の実証に成功 ―非自明なスピン配列による新機構、磁気情報の読み出し方法として期待―

2026-05-27 東京大学

立体的なスピン配列の反強磁性秩序を磁気光学効果により読み出している模式図

＜関連情報＞

• https://www.t.u-tokyo.ac.jp/press/pr2026-05-27-001
• https://www.nature.com/articles/s41467-026-72889-5

非共面反強磁性体における巨大なトポロジカル磁気光学効果 Giant topological magneto-optical effect in noncoplanar antiferromagnet

Y. Okamura,Y. Hayashi,N. D. Khanh,Y. Tokura,S. Seki & Y. Takahashi
Nature Communications  Published:27 May 2026
DOI:https://doi.org/10.1038/s41467-026-72889-5

Abstract

Geometrical frustration on triangular lattice is expected to exhibit diverse quantum spin and electronic states endowed with emergent electromagnetic phenomena. The all-in-all-out (AIAO)-type antiferromagnetic spin structure is one such example, possessing the scalar spin chirality that generates giant emergent magnetic field with vanishingly small magnetization. Here, we report on the large spontaneous magneto-optical Kerr effect (MOKE) caused by the AIAO/AOAI state in quasi-two-dimensional triangular-lattice compound CoNb₃S₆. Over the entire measured energy region from 55 to 2000 meV, the MOKE is found to be dominated only by the spin chirality. Essential role of momentum-space Berry curvature for both MOKE and dc Hall effect is demonstrated by the spectral analysis of optical Hall conductivity derived from MOKE. The figure of merit of observed topological MOKE, light-polarization rotation angle divided by magnetization, largely exceeds other magnets including time-reversal-symmetry broken antiferromagnet Mn₃Sn. Our findings demonstrate the strong light-spin coupling through the spin chirality, paving the way for antiferromagnetic spintronics and future optospintronic devices.