Observation of Altermagnetic Order Switching in Bulk MnTe by Polarized Neutron Diffraction
ORAL
Abstract
Altermagnets enable efficient non-relativistic spin current generation without stray fields, offering potential for the miniaturization of spintronic devices [1]. The altermagnetic order, characterized by the Néel vector in altermagnet, is insensitive to the magnetic-field control because of the zero net magnetization. However, further inclusion of relativistic spin-orbit coupling alters this paradigm: weak ferromagnetic moment (WFM) is theoretically anticipated to emerge with the altermagnetic order [2, 3], thereby enabling the magnetic-field control of altermagnetic antiphase domain. This establishes WFM as a promising broadly applicable mechanism for controlling altermagnetic order. In altermagnetic MnTe, spin–orbit–induced feedback of the magnetic order slightly lowers the symmetry from P63/mmc to Cmcm—preserving inversion but breaking the threefold rotation—which allows otherwise cancelling Dzyaloshinskii–Moriya–type terms on interlayer Mn–Mn bonds to acquire a tiny net component and thereby couple the minute weak‑ferromagnetic canting to the altermagnetic order [2]. The WFM in MnTe generates negligible stray field but enable the field-selection of magnetic antiphase domain states.
The time-reversal symmetry breaking in altermagnets results in non-zero nuclear-magnetic interference (NMI) [4], which is a direct manifest of the altermagnetic order. In this study, pronounced NMI was observed in MnTe bulk crystal by polarized neutron diffraction (PoND). The sign of NMI was reversed by field cooling with opposite magnetic field in milli-Tesla-scale, suggesting the switching of altermagnetic order. By further remanent magnetization measurements, the WFM was confirmed to be associate with the distribution of antiphase domains. These findings realized a general route for the magnetic control of altermagnetic order via flipping the WFM. Furthermore, we demonstrate PoND as a powerful bulk-sensitive probe of altermagnetic order, complementing the local detection techniques like scanning tunneling microscopy, which are limited to the surfaces or thin films.
[1] L. Šmejkal et al., Phys. Rev. X 12, 031042 (2022).
[2] I. I. Mazin et al., Phys. Rev. B 110, 214436 (2024).
[3] M. Roig et al., Phys. Rev. Lett. 135, 016703 (2025).
[4] P. A. McClarty et al., Phys. Rev. B 111, L060405 (2025).
The time-reversal symmetry breaking in altermagnets results in non-zero nuclear-magnetic interference (NMI) [4], which is a direct manifest of the altermagnetic order. In this study, pronounced NMI was observed in MnTe bulk crystal by polarized neutron diffraction (PoND). The sign of NMI was reversed by field cooling with opposite magnetic field in milli-Tesla-scale, suggesting the switching of altermagnetic order. By further remanent magnetization measurements, the WFM was confirmed to be associate with the distribution of antiphase domains. These findings realized a general route for the magnetic control of altermagnetic order via flipping the WFM. Furthermore, we demonstrate PoND as a powerful bulk-sensitive probe of altermagnetic order, complementing the local detection techniques like scanning tunneling microscopy, which are limited to the surfaces or thin films.
[1] L. Šmejkal et al., Phys. Rev. X 12, 031042 (2022).
[2] I. I. Mazin et al., Phys. Rev. B 110, 214436 (2024).
[3] M. Roig et al., Phys. Rev. Lett. 135, 016703 (2025).
[4] P. A. McClarty et al., Phys. Rev. B 111, L060405 (2025).
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Presenters
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Zheyuan Liu
- Univ of Tokyo