量子センサーで“見えない磁石”の構造を解明 ～八極子磁壁の正体に迫る～

2025-07-18 東京大学

ダイヤモンド量子センサによる八極子磁壁の高精度測定
磁気八極子（六角形）の秩序方向（青と赤の向き）が空間的に変化している構造（磁壁）の測定イメージ。磁気八極子は6つの磁気双極子（六芒星の各頂点の灰色矢印）から構成されています。ナノスケールの量子センサを物質表面で走査して計測することで、八極子の空間的な構造を明らかにしました。

＜関連情報＞

• https://www.s.u-tokyo.ac.jp/ja/press/10846/
• https://journals.aps.org/prb/abstract/10.1103/njnm-nl6n

八極子秩序反強磁性体におけるキラル磁壁の観測 Observation of chiral domain walls in an octupole-ordered antiferromagnet

Moeta Tsukamoto, Zhewen Xu, Tomoya Higo, Kouta Kondou, Kento Sasaki, Mihiro Asakura, Shoya Sakamoto, Pietro Gambardella, Shinji Miwa et al.
Physical Review B  Published: 17 July, 2025
DOI: https://doi.org/10.1103/njnm-nl6n

Abstract

Spin chirality in antiferromagnets offers new opportunities for spintronics. The kagome antiferromagnet Mn₃⁢Sn is a paradigmatic material in which the antiferromagnetic order parameter can be detected and controlled by electrical means. However, direct investigation of the magnetic texture of Mn₃⁢Sn has been challenging because of the tiny moment hosted in its magnetic octupole, hindering further clarification of this unique material. Here, we address this issue by observing the stray magnetic field from Mn₃⁢Sn using a diamond-based quantum scanning microscope. The spatially resolved intrinsic domains and domain walls in a high-quality single-crystalline Mn₃⁢Sn film quantitatively reveal the polarization angle of the magnetic octupole in the kagome plane, the domain’s local magnetization, the domain wall’s width and chirality, and the octupole order in domain walls. Our nanoscale investigation of Mn₃⁢Sn, a powerful complement to macroscopic measurements, paves the road for developing chiral antiferromagnetism and its potential for spintronic applications.