We identified and exploited a novel mechanism in an emerging branch of spintronics based on transport phenomena governed by crystal and magnetic symmetries, and its interplay with the antiferromagnetic order [1]. In this talk, we will focus on the origin of the subsequent experimental observation of a large spontaneous Hall effect in the Mn5Si3 antiferromagnet, arising mostly by time-reversal symmetry breaking. These findings could prove essential for the development of robust large effects, vital in new device concepts. More specifically, the Zeeman effect is among the cornerstones of quantum physics that contributed to the development of spintronics. To date, the Zeeman spin-splitting of atomic energy levels or bands in crystals has been associated with the presence of a magnetic dipole. Countering the established physical picture [2-4], we identify an antiferromagnet with a band-structure comprised of separated crystal-momentum valleys with opposite Zeeman spin-splittings, which allows for their probing and exploiting by analogous electron-transport phenomena as used for the Zeeman effect in the presence of the magnetic dipole. In this talk we focus on one of the most prominent consequences of spin splitting – the spontanous Hall effect. We experimentally demonstrated its presence in Mn5Si3 an antiferromagnet with separated Zeeman spin-split valleys [1]. We carefully disentangled various contributions to the measured transversal signal and we show that the signal is dominated by a robust spontaneous (present at zero magnetic field) Hall contribution with broad coercivity, which can only be attributed to the antiferromagnetic Zeeman effect. We further present structural, magnetization and magneto-transport results in a sample series and discuss the role of epitaxial growth on our results.

**References:**

[1] H. Reichlova, R. L. Seeger et al, under review. arXiv:2012.15651 [2] L. Néel. Magnetism and Local Molecular Field. Science 174, 985-992 (1971). [3] N. J. Ghimire et al. Large anomalous Hall effect in the chiral-lattice antiferromagnet CoNb3S6. Nat. Com. 9, 3280 (2018). [4] C. Sürgers, et al. Large topological Hall effect in the non-collinear phase of an antiferromagnet. Nat. Com. 5, 3400 (2014).

**Images:**

 Spontaneous Hall effect in the Mn5Si3 antiferromagnet, due to antiferromagnetic Zeeman spin-splitting

In this work some results of the investigation of the new crystalline Hall effect, proposed by Libor et. al., in the compound CoNb3S6 for the antiferromagnetic collinear phase are presented. The electronic properties of the compound are determined by first principle methods, including orbital spin coupling. The topological properties present in the band structure of the crystal were analyzed and the presence of an "Hourglass" dispersion relation was found, due to the presence of non-symmetrical rotation symmetry axes. The relationship between the symmetries of the compound and the conductivity tensor was also analyzed, finding that the point magnetic group of the antiferromagnetic compound with Néel vector [100] is 2'2'2, so the conductivity tensor indicates the presence of a crystalline Hall effect. Using Wannier functions and Kubo equation, the Berry curvature and anomalous Hall conductivity were derived. Being a collinear antiferromagnetic material, a zero Hall conductivity would be expected for all components, but due to the spontaneous break of symmetry generated by the non-magnetic sulfur atoms surrounding the cobalt atoms, an anomalous Hall conductivity appears, which could be explained by the proposed mechanism of the crystalline Hall effect.

Crystal Hall Effect in Collinear Antiferromagnets: symmetry and first principles analysis of CoNb3S6

*Session Chair: Samik DuttaGupta, Tohoku University*

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FG: Antiferromagnetic Spintronics I

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The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.

Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. 

Rafael Gonzalez-Hernandez

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Presentations

Spontaneous Hall effect in the Mn5Si3 antiferromagnet, due to antiferromagnetic Zeeman spin-splitting

Crystal Hall Effect in Collinear Antiferromagnets: symmetry and first principles analysis of CoNb3S6

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