Visualizing Magnetic Structure in 3D Nanoscale Ni-Fe Gyroid Networks

Justin Llandro; David M Love; András Kovács; Jan Caron; Kunal N Vyas; Attila Kákay; Ruslan Salikhov; Kilian Lenz; Jürgen Fassbender; Maik R J Scherer; Christian Cimorra; Ullrich Steiner; Crispin H W Barnes; Rafal E Dunin-Borkowski; Shunsuke Fukami; Hideo Ohno

doi:10.1021/acs.nanolett.0c00578

Visualizing Magnetic Structure in 3D Nanoscale Ni-Fe Gyroid Networks

Nano Lett. 2020 May 13;20(5):3642-3650. doi: 10.1021/acs.nanolett.0c00578. Epub 2020 Apr 10.

Authors

Justin Llandro^{1

2

3}, David M Love⁴, András Kovács⁵, Jan Caron⁵, Kunal N Vyas⁴, Attila Kákay⁶, Ruslan Salikhov⁶, Kilian Lenz⁶, Jürgen Fassbender^{6

7}, Maik R J Scherer⁴, Christian Cimorra⁴, Ullrich Steiner⁸, Crispin H W Barnes⁴, Rafal E Dunin-Borkowski⁵, Shunsuke Fukami^{1

2

3

9

10}, Hideo Ohno^{1

2

3

9

10}

Affiliations

¹ Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
² Center for Spintronics Research Network, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
³ Center for Science and Innovation in Spintronics, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
⁴ Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
⁵ Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany.
⁶ Helmholtz-Zentrum Dresden - Rossendorf (HZDR), Bautzner Landstrasse 400, 01328 Dresden, Germany.
⁷ Technische Universität Dresden, Haeckelstrasse 3, 01069 Dresden, Germany.
⁸ Adolphe Merkle Institute, Chemin des Verdiers 4, 1700 Fribourg, Switzerland.
⁹ Center for Innovative Integrated Electronic Systems, Tohoku University, 468-1 Aramaki Aza Aoba, Aoba-ku, Sendai 980-0845 Japan.
¹⁰ WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.

PMID: 32250635
DOI: 10.1021/acs.nanolett.0c00578

Abstract

Arrays of interacting 2D nanomagnets display unprecedented electromagnetic properties via collective effects, demonstrated in artificial spin ices and magnonic crystals. Progress toward 3D magnetic metamaterials is hampered by two challenges: fabricating 3D structures near intrinsic magnetic length scales (sub-100 nm) and visualizing their magnetic configurations. Here, we fabricate and measure nanoscale magnetic gyroids, periodic chiral networks comprising nanowire-like struts forming three-connected vertices. Via block copolymer templating, we produce Ni₇₅Fe₂₅ single-gyroid and double-gyroid (an inversion pair of single-gyroids) nanostructures with a 42 nm unit cell and 11 nm diameter struts, comparable to the exchange length in Ni-Fe. We visualize their magnetization distributions via off-axis electron holography with nanometer spatial resolution and interpret the patterns using finite-element micromagnetic simulations. Our results suggest an intricate, frustrated remanent state which is ferromagnetic but without a unique equilibrium configuration, opening new possibilities for collective phenomena in magnetism, including 3D magnonic crystals and unconventional computing.

Keywords: gyroids; magnetic metamaterials; off-axis electron holography; transmission electron microscopy.