Chiral Magnetism and High-Temperature Skyrmions in B20-Ordered Co-Si

Balamurugan Balasubramanian, Priyanka Manchanda, Rabindra Pahari, Zhen Chen, Wenyong Zhang, Shah R. Valloppilly, Xingzhong Li, Anandakumar Sarella, Lanping Yue, Ahsan Ullah, Pratibha Dev, David A. Muller, Ralph Skomski, George C. Hadjipanayis, and David J. Sellmyer

Phys. Rev. Lett. 124, 057201 – Published 6 February 2020

Abstract

Magnets with chiral crystal structures and helical spin structures have recently attracted much attention as potential spin-electronics materials, but their relatively low magnetic-ordering temperatures are a disadvantage. While cobalt has long been recognized as an element that promotes high-temperature magnetic ordering, most Co-rich alloys are achiral and exhibit collinear rather than helimagnetic order. Crystallographically, the B20-ordered compound CoSi is an exception due to its chiral structure, but it does not exhibit any kind of magnetic order. Here, we use nonequilibrium processing to produce B20-ordered ${Co}_{1 + x} {Si}_{1 - x}$ with a maximum Co solubility of $x = 0.043$ . Above a critical excess-Co content ( $x_{c} = 0.028$ ), the alloys are magnetically ordered, and for $x = 0.043$ , a critical temperature $T_{c} = 328 K$ is obtained, the highest among all B20-type magnets. The crystal structure of the alloy supports spin spirals caused by Dzyaloshinskii-Moriya interactions, and from magnetic measurements we estimate that the spirals have a periodicity of about 17 nm. Our density-functional calculations explain the combination of high magnetic-ordering temperature and short periodicity in terms of a quantum phase transition where excess-cobalt spins are coupled through the host matrix.

Received 17 June 2019
Accepted 3 January 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.057201

Physics Subject Headings (PhySH)

Magnetic order Magnetism Spintronics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Balamurugan Balasubramanian ^1,2,*, Priyanka Manchanda³, Rabindra Pahari ^1,2, Zhen Chen ⁴, Wenyong Zhang^1,2, Shah R. Valloppilly¹, Xingzhong Li¹, Anandakumar Sarella ¹, Lanping Yue ^1,2, Ahsan Ullah ^1,2, Pratibha Dev³, David A. Muller⁴, Ralph Skomski^1,2, George C. Hadjipanayis⁵, 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
⁴School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
⁵Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA