Topological magneto-optical effects and their quantization in noncoplanar antiferromagnets

Wang, Feng; Hanke, Jan-Philipp; Zhou, Xiaodong; Guo, Guang‐Yu; Blügel, Stefan; Mokrousov, Yuriy; Yao, Yugui

doi:10.1038/s41467-019-13968-8

Cited by 74 publications

(49 citation statements)

References 65 publications

(54 reference statements)

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“…In addition to these coplanar antiferromagnetic metals, Feng et al recently identified compensated non-coplanar orderings as candidates for strong MOKE signals and illustrate this using first-principles results for Kerr rotation angles of γ-Fe 0.5 Mn 0.5 . 174 Most of the above results focus on polar MOKE, i.e., MOKE for surfaces perpendicular to the direction characterizing magnetic ordering, e.g. that of weak magnetization.…”

Section: And 156mentioning

confidence: 99%

Metallic antiferromagnets

Siddiqui¹,

Sklenar²,

Kang³

et al. 2020

Journal of Applied Physics

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Antiferromagnet materials have recently gained renewed interest due to their possible use in spintronics technologies, where spin transport is the foundation of their functionalities. In that respect metallic antiferromagnets are of particular interest, since they enable complex interplays between electronic charge transport, spin, optical, and magnetization dynamics. Here we review phenomena where the metallic conductivity provides unique perspectives for the practical use and fundamental properties of antiferromagnetic materials. II. CHARGE TRANSPORT IN METALLIC ANTIFERROMAGNETS A. MagnetoresistanceAnisotropic magnetoresistance (AMR) is a long-studied electrical property of ferromagnetic metals where resistivity depends upon the relative orientation between current and magnetization. 13 In spintronics research involving ferromag-arXiv:2005.05247v1 [cond-mat.str-el] 11 May 2020 state (see Fig. 1). In the Fe 2 O 3 /Pt bilayer system, intentional thermal annealing of the sample was used to distinguish two distinct types of switching in the magnetoresistance. A sawtooth magnetoresistance shape was attributed to the thermal artifact, while a smaller amplitude step-like change in the resistance was identified as antiferromagnetic switching. The implications of these new SMR switching experiments have not been fully reconciled yet with the earlier AMR switching experiments. Clearly, a future goal in the field of antiferromagnetic spintronics will be to identify and separate magnetoresistance effects arising from thermal or electromigration artifacts in both SMR and AMR based systems and devices.

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Section: And 156mentioning

confidence: 99%

Metallic antiferromagnets

Siddiqui¹,

Sklenar²,

Kang³

et al. 2020

Journal of Applied Physics

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“…Moreover, the noncoplanar spin structures can generate the so-called emergent electromagnetic fields through the Berry phase mechanism [4,24,[28][29][30][31]. They are fictitious electromagnetic fields acting on electrons coupled to the spin textures, and thus, give rise to unusual quantum transport and optical phenomena, such as the topological Hall effect [32][33][34][35][36][37], the Nernst effect [38][39][40], the magneto-optical Kerr effect [41,42], and the emergent inductance [43][44][45][46][47]. Owing to these distinguishing properties, the topological spin textures have attracted a lot of attention for not only fundamental physics but also applications to next-generation electronic devices.…”

Section: Introductionmentioning

confidence: 99%

Phase degree of freedom and topology in multiple-$Q$ spin textures

Shimizu,

Okumura,

Kato

et al. 2022

Preprint

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A periodic array of topological spin textures, such as skyrmions and hedgehogs, is called the multiple-Q spin texture, as it is represented by a superposition of multiple spin density waves. Depending on the way of superposition, not only the magnetic but also the topological properties are modified, leading to a variety of quantum transport and optical phenomena caused by the emergent electromagnetic fields through the Berry phase. Among others, the phase degree of freedom of the superposed waves is potentially important for such modifications, but its effect has not been fully investigated thus far. Here we perform systematic theoretical analyses of magnetic and topological properties of the multiple-Q spin textures with the phase degree of freedom in two and three dimensions. By introducing a hyperspace with an additional dimension corresponding to the phase degree of freedom, we establish a generic framework to deal with the phase shift in the multiple-Q spin textures. Using the hyperspace representation, we elaborate the complete topological phase diagrams for the superpositions of three proper screws or sinusoidal waves in two dimensions and those of four in three dimensions. In the two-dimensional case, we find that the phase shift as well as the magnetization change can yield the skyrmion lattices with the skymion number of −2, −1, 1, and 2, corresponding to the evolution of the Dirac strings connecting hedgehogs and antihedgehogs in the three-dimensional hyperspace. We show that the high skyrmion numbers ±2 appear in wider parameter regions for the sinusoidal superpositions than the screw ones. Meanwhile, in the three-dimensional case, we clarify that the topological phase diagrams include various types of the hedgehog lattices whose total number of hedgehogs and antihedgehogs ranges up to 48 in a cubic unit. Interestingly, the phase shift can generate unusual Dirac strings running on the horizontal planes perpendicular to the magnetization direction, which gives rise to unconventional pair creation of hedgehogs and antihedgehogs while increasing the magnetization in the case of the screw superpositions. We also show that the amplitude of the emergent magnetic field is maximized by fusion of hedgehogs and antihedgehogs on the horizontal Dirac strings in both proper screw and sinusoidal cases. In addition, by analyzing the numerical data in the previous studies, we demonstrate that phase shifts are indeed caused by an external magnetic field, associated with the topological transitions in the multiple-Q spin textures. Our results illuminate the topological aspects of the skyrmion and hedgehog lattices with the phase degree of freedom, which would be extended to other multiple-Q textures and useful for the exploration of topologically nontrivial magnetic phases and exotic quantum phenomena.

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“…Magnetic topological states are currently attracting widespread interest in condensed matter physics with a variety of exotic topological phenomena constantly proposed and intensively explored [1,2], and in which, the anomalous Hall effect [3][4][5][6][7], spin-orbit torques [8], magneto-optical effect [9,10], and Dzyaloshinskii-Moriya interaction [11,12] can exceed by far that of conventional compounds, suggesting a huge potential for spintronic devices. Antiferromagnetic (AFM) topological insulator (TI) [13], a conceptual milestone, has been demonstrated in three-dimensional (3D) MnBi 2n Te 3n+1 (n = 1, 2, 3) family of materials with axion topology and Möbius fermion ensured by a combined symmetry T T 1/2 , where T is the time-reversal symmetry and T 1/2 represents the half primitive-lattice translation [14][15][16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Antiferromagnetic topological crystalline insulator and mixed Weyl semimetal in two-dimensional NpAs monolayer

Zou

Mao

et al. 2021

New J. Phys.

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Magnetic topological states have attracted significant attentions due to their intriguing quantum phenomena and potential applications in topological spintronic devices. Here, we propose a two-dimensional material NpAs monolayer as a candidate for multiple topological states accompanied with the changes of magnetic structures. Under the antiferromagnetic configuration, the long-awaited topological crystalline insulator (TCI) emerges with a nonzero mirror Chern number $\mathcal{C_M} = 1$ and a giant band gap of 630 meV, and remarkably a pair of gapless edge states can be tailored by rotating the magnetization directions while the TCI phase survives. Moreover, we establish the existence of quantum anomalous Hall effect and nontrivial nodal points under the ferromagnetic configuration, thereby giving rise to the mixed Weyl semimetal after adding the magnetization direction to topological classification. Our findings not only provide an ideal candidate for uncovering exotic topological characters with magnetism but also put forward potential applications in topological spintronics.

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Topological magneto-optical effects and their quantization in noncoplanar antiferromagnets

Cited by 74 publications

References 65 publications

Metallic antiferromagnets

Metallic antiferromagnets

Phase degree of freedom and topology in multiple-$Q$ spin textures

Antiferromagnetic topological crystalline insulator and mixed Weyl semimetal in two-dimensional NpAs monolayer

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