Soft-Magnetic Skyrmions Induced by Surface-State Coupling in an Intrinsic Ferromagnetic Topological Insulator Sandwich Structure

Takuya Takashiro; Ryota Akiyama; Ivan A Kibirev; Andrey V Matetskiy; Ryosuke Nakanishi; Shunsuke Sato; Takuro Fukasawa; Taisuke Sasaki; Haruko Toyama; Kota L Hiwatari; Andrey V Zotov; Alexander A Saranin; Toru Hirahara; Shuji Hasegawa

doi:10.1021/acs.nanolett.1c02952

Soft-Magnetic Skyrmions Induced by Surface-State Coupling in an Intrinsic Ferromagnetic Topological Insulator Sandwich Structure

Nano Lett. 2022 Feb 9;22(3):881-887. doi: 10.1021/acs.nanolett.1c02952. Epub 2022 Jan 27.

Affiliations

¹ Department of Physics, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan.
² Institute of Automation and Control Processes, Vladivostok 690041, Russia.
³ Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan.
⁴ National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.

PMID: 35084202
DOI: 10.1021/acs.nanolett.1c02952

Abstract

A magnetic skyrmion induced on a ferromagnetic topological insulator (TI) is a real-space manifestation of the chiral spin texture in the momentum space and can be a carrier for information processing by manipulating it in tailored structures. Here, a sandwich structure containing two layers of a self-assembled ferromagnetic septuple-layer TI, Mn(Bi_1-xSb_x)₂Te₄ (MnBST), separated by quintuple layers of TI, (Bi_1-xSb_x)₂Te₃ (BST), is fabricated and skyrmions are observed through the topological Hall effect in an intrinsic magnetic topological insulator for the first time. The thickness of BST spacer layer is crucial in controlling the coupling between the gapped topological surface states in the two MnBST layers to stabilize the skyrmion formation. The homogeneous, highly ordered arrangement of the Mn atoms in the septuple-layer MnBST leads to a strong exchange interaction therein, which makes the skyrmions "soft magnetic". This would open an avenue toward a topologically robust rewritable magnetic memory.

Keywords: chiral spin state; ferromagnetic topological insulator; ferromagnetism; heterostructure; skyrmion; topological Hall effect; topological insulator.