Controlled skyrmion nucleation in extended magnetic layers using a nanocontact geometry

Philipp Dürrenfeld, Yongbing Xu, Johan Åkerman, and Yan Zhou

Phys. Rev. B 96, 054430 – Published 22 August 2017

Abstract

We propose and numerically simulate a spintronic device layout consisting of a nanocontact on top of an extended Co/Pt bilayer. The interfacial Dzyaloshinskii-Moriya interaction in such bilayer systems can lead to the possible existence of metastable skyrmions. A small dc current injected through the nanocontact enables the manipulation of the size as well as the annihilation of an initially present skyrmion, while ps-long current pulses allow for the controlled nucleation of single skyrmions underneath the nanocontact. The results are obtained from micromagnetic simulations and can be potentially used for future magnetic storage implementations.

Received 13 March 2017

DOI:https://doi.org/10.1103/PhysRevB.96.054430

Physics Subject Headings (PhySH)

Dzyaloshinskii-Moriya interaction Skyrmions

Ultrathin films

Micromagnetic modeling

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Philipp Dürrenfeld¹, Yongbing Xu^1,2,*, Johan Åkerman^3,4, and Yan Zhou^5,†

¹Jiangsu Provincial Key Laboratory of Nanotechnology, School of Electronic Science and Engineering, Nanjing University, 210093 Nanjing, China
²York-Nanjing International Center of Spintronics, Department of Electronics, The University of York, YO10 3DD York, England, United Kingdom
³Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden
⁴Materials and Nanophysics, School of ICT, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden
⁵School of Science and Engineering, The Chinese University of Hong Kong, 518172 Shenzhen, China

^*ybxu@nju.edu.cn
^†zhouyan@cuhk.edu.cn

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Issue

Vol. 96, Iss. 5 — 1 August 2017

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Images

Figure 1
(a) Schematics of the simulated layout with a 30-nm-diameter NC and current flowing radially away from it. Color represents the in-plane current density in the Pt layer. Inset: 30-ps current pulses are used to write single skyrmions underneath the NC. (b) In-plane current density as a function of distance from the NC center for four different diameters and out-of-plane current density for a 30-nm diameter, all calculated for a 1-mA current. Inset: Maximum current density $J_{peak}$ as a function of inverse NC diameter.
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Figure 2
(a) Skyrmion radius as a function of an applied perpendicular field and DMI strength. (b) Radius of a skyrmion placed underneath the NC ( $D_{ind} = 2 mJ / m^{2}$ and zero field) and subjected to a small current. Inset: Trajectory of a skyrmion in the vicinity of the NC that gets attracted by a current of 0.5 mA. The blue squares are placed in time intervals of 1 ns.
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Figure 3
Skyrmion nucleation with a current pulse of $- 22$ mA. (a)–(f) Time snapshots of the nucleation process. Color denotes the $z$ component of the normalized magnetization ( $m_{z}$ ) and the arrows relate to the in-plane direction of the magnetization. (g) Plot of averaged $m_{z}$ and $S$ as a function of time. The current pulse is applied between 0 and 0.03 ns. The dashed lines mark the times of (c)–(f). (h) Nucleation time until a fully relaxed skyrmion is formed as a function of the current pulse amplitude for zero field and 5 mT.
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Figure 4
Writing time of a single skyrmion with 30-ps-long current pulses in a 5-mT external field as a function of the pulse amplitude for four different NC diameters. The most left point of each data set represents the threshold current. Inset: The minimum required $J_{peak}$ for successful nucleation as a function of NC diameter.
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Figure 5
(a) Writing time of a single skyrmion underneath a 30-nm-diameter NC and with a 5-mT external field as a function of the pulse amplitude for five different pulse lengths. The most left point of each data set represents the threshold current. (b) The minimum required $J_{peak}$ (black squares) as well as the minimum writing energy (red diamonds) for the successful skyrmion nucleation as a function of the pulse duration.
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Figure 6
Writing of an additional skyrmion into an already present structure with four skyrmions initially placed 150 nm away from the NC. $I_{pulse} = - 22 mA$ , $D_{ind} = 2 mJ / m^{2}$ , and an out-of-plane field of 5 mT are used.
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