近日，日本东京大学的S.Seki课题组在一项最新研究中，成功发现了插层范德华材料中非共面反铁磁序诱导的自发拓扑霍尔效应。相关研究成果已于2023年4月20日在国际知名学术期刊《自然—物理学》上发表。
该研究团队发现了三角晶格化合物CoTa3S6 和 CoNb3S6中的全内部-全外部型非共面反铁磁序。虽然这些化合物的净磁化非常小，但据报道，它们承载了非传统的大自发霍尔效应。通过分析发现，这种效应可以通过与标量自旋手性相关的虚拟磁场所产生的拓扑霍尔效应来解释。这些结果表明，标量自旋手性机制提供了一个有前途的途径来实现即使在补偿反铁磁体中也具有巨大自发霍尔响应，并强调了插层范德华磁体作为一个有前途的准二维材料平台，可以实现各种非平凡的电读取方式和可能的非共面反铁磁域编写。
研究人员指出，在铁磁体中，电流通常会引起与内部磁化成比例的横向霍尔电压，这种效应经常用于自旋↑和自旋↓状态的电读取。尽管反铁磁体通常不具备这些特性，但最近的理论研究预测，非共面反铁磁序具有有限标量自旋手性，即相邻自旋之间跨越的固体角度，可以在没有净磁化或外部磁场的情况下引起大的自发霍尔效应。这种现象被称为自发拓扑霍尔效应，可以潜在地用于高效的反铁磁态电读取。然而，由于缺乏适当的材料来承载这种磁性，这种效应尚未得到实验验证。
附：英文原文
Title: Spontaneous topological Hall effect induced by non-coplanar antiferromagnetic order in intercalated van der Waals materials
Author: Takagi, H., Takagi, R., Minami, S., Nomoto, T., Ohishi, K., Suzuki, M.-T., Yanagi, Y., Hirayama, M., Khanh, N. D., Karube, K., Saito, H., Hashizume, D., Kiyanagi, R., Tokura, Y., Arita, R., Nakajima, T., Seki, S.
Issue&Volume: 2023-04-20
Abstract: In ferromagnets, an electric current generally induces a transverse Hall voltage in proportion to the internal magnetization. This effect is frequently used for the electrical readout of the spin-↑ and spin-↓ states. Although these properties are usually not expected in antiferromagnets, recent theoretical studies predicted that a non-coplanar antiferromagnetic order with finite scalar spin chirality—meaning a solid angle spanned by neighbouring spins—can induce a large spontaneous Hall effect even without a net magnetization or external magnetic field. This phenomenon—the spontaneous topological Hall effect—can potentially be used for the efficient electrical readout of antiferromagnetic states, but it has not been experimentally verified due to a lack of appropriate materials hosting such magnetism. Here we report the discovery of an all-in–all-out-type non-coplanar antiferromagnetic order in triangular lattice compounds CoTa3S6 and CoNb3S6. These compounds are reported to host unconventionally large spontaneous Hall effects despite their vanishingly small net magnetization, and our analysis reveals that it can be explained in terms of the topological Hall effect that originates from the fictitious magnetic field associated with scalar spin chirality. These results indicate that the scalar spin chirality mechanism offers a promising route to the realization of a giant spontaneous Hall response even in compensated antiferromagnets, and highlight intercalated van der Waals magnets as a promising quasi-two-dimensional material platform to enable various non-trivial ways of electrical reading and the possible writing of non-coplanar antiferromagnetic domains.
DOI: 10.1038/s41567-023-02017-3
Source: https://www.nature.com/articles/s41567-023-02017-3