Peripheral chiral spin textures and topological Hall effect in CoSi nanomagnets

Rabindra Pahari, Balamurugan Balasubramanian, Ahsan Ullah, Priyanka Manchanda, Hiroaki Komuro, Robert Streubel, Christoph Klewe, Shah R. Valloppilly, Padraic Shafer, Pratibha Dev, Ralph Skomski, and David J. Sellmyer

Phys. Rev. Materials 5, 124418 – Published 29 December 2021

Abstract

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.

Received 14 April 2021
Accepted 10 December 2021

DOI:https://doi.org/10.1103/PhysRevMaterials.5.124418

Physics Subject Headings (PhySH)

Magnetism Skyrmions Topological Hall effect

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Rabindra Pahari ^1,2,*, Balamurugan Balasubramanian^1,2, Ahsan Ullah^1,2, Priyanka Manchanda³, Hiroaki Komuro ^1,4, Robert Streubel^1,2, Christoph Klewe⁵, Shah R. Valloppilly¹, Padraic Shafer⁵, Pratibha Dev ³, Ralph Skomski^1,2, and David J. Sellmyer^1,2,†

¹Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
²Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588, USA
³Department of Physics and Astronomy, Howard University, Washington, DC, 20059, USA
⁴Department of Cardiovascular Medicine, Tokyo Medical and Dental University, Tokyo 113-8510, Japan
⁵Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^*Present address: Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
^†Corresponding author: dsellmyer@unl.edu