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The spin structure and transport behavior of B20-ordered CoSi nanomagnets are investigated experimentally and by theoretical calculations. B20 materials are of interest in spin electronics because their noncentrosymmetric crystal structure favors noncoplanar spin structures that yield a contribution to the Hall effect. However, stoichiometric bulk CoSi is nonmagnetic, and combining magnetic order at and above room temperature with small feature sizes has remained a general challenge. Our CoSi nanoclusters have an average size of 11.6 nm and a magnetic ordering temperature of 330 K. First-principle calculations and x-ray circular dichroism experiments show that the magnetic moment is predominantly confined to the shells of the clusters. The CoSi nanocluster ensemble exhibits a topological Hall effect, which is explained by an analytical model and by micromagnetic simulations on the basis of competing Dzyaloshinskii-Moriya and intra- and intercluster exchange interactions. The topological Hall effect is caused by formation of chiral spin textures in the shells of the clusters, which exhibit fractional skyrmion number and are therefore termed as paraskyrmions (closely related to skyrmion spin structures). This research shows how nanostructuring of a chiral atomic structure can create a spin-textured material with a topological Hall effect and a magnetic ordering temperature above room temperature.
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Magnetism and topological Hall effect in antiferromagnetic Ru2MnSn-based Heusler compounds
Heusler compounds and alloys based on them are of great recent interest because they exhibit a wide variety of spin structures, magnetic properties, and electron-transport phenomena. Their properties are tunable by alloying and we have investigated L21-orderd compound Ru2MnSn and its alloys by varying the atomic Mn:Sn composition. While antiferromagnetic ordering with a Néel temperature of 361 K was observed in Ru2MnSn, the Mn-poor Ru2Mn0.8Sn1.2 alloy exhibits properties of a diluted antiferromagnet in which there are localized regions of uncompensated Mn spins. Furthermore, a noncoplanar spin structure, evident from a topological Hall-effect contribution to the room-temperature Hall resistivity, is realized in Ru2Mn0.8Sn1.2. Our combined experimental and theoretical analysis shows that in the Ru2Mn0.8Sn1.2 alloy, the magnetic properties can be explained in terms of a noncoplanar antiferromagnetic scissor mode, which creates a small net magnetization in a magnetic field and subsequently yields a Berry curvature with a strong topological Hall effect.
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- PAR ID:
- 10313622
- Date Published:
- Journal Name:
- Journal of magnetism and magnetic materials
- Volume:
- 537
- ISSN:
- 0304-8853
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1016/j.jmmm.2021.168104
