Phys. Rev. X 5, 041049 (2015)

Open Access

Spin-Wave Diode

Jin Lan (兰金), Weichao Yu (余伟超), Ruqian Wu, and Jiang Xiao (萧江)

Phys. Rev. X 5, 041049 – Published 28 December 2015

Abstract

A diode, a device allowing unidirectional signal transmission, is a fundamental element of logic structures, and it lies at the heart of modern information systems. The spin wave or magnon, representing a collective quasiparticle excitation of the magnetic order in magnetic materials, is a promising candidate for an information carrier for the next-generation energy-saving technologies. Here, we propose a scalable and reprogrammable pure spin-wave logic hardware architecture using domain walls and surface anisotropy stripes as waveguides on a single magnetic wafer. We demonstrate theoretically the design principle of the simplest logic component, a spin-wave diode, utilizing the chiral bound states in a magnetic domain wall with a Dzyaloshinskii-Moriya interaction, and confirm its performance through micromagnetic simulations. Our findings open a new vista for realizing different types of pure spin-wave logic components and finally achieving an energy-efficient and hardware-reprogrammable spin-wave computer.

Received 31 July 2015

DOI:https://doi.org/10.1103/PhysRevX.5.041049

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Authors & Affiliations

Jin Lan (兰金)¹, Weichao Yu (余伟超)¹, Ruqian Wu^1,2, and Jiang Xiao (萧江)^1,3,*

¹Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
²Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA
³Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433, China

^*Corresponding author. xiaojiang@fudan.edu.cn

Popular Summary

Magnonics, which involves unified information storage and processing using magnons—spin waves that are collective quasiparticle excitations of magnetic moments—offers a promising platform for next-generation, energy-saving information technology. Many magnonic structures have been proposed and studied in a range of designs, but a unified and scalable magnonic platform is still lacking. Here, we propose the design of magnonic integrated circuits that can, in principle, perform a large number of magnonic operations.

We use domain walls and surface anisotropy stripes as two different spin-wave waveguides. The magnonic integrated circuits that we design include a single square magnetic wafer, which is analogous to a silicon wafer. We conduct simulations with yttrium iron garnet thin-film magnetic wafers of several sizes (roughly a few thousand nanometers on a side). Since the circuits are built upon magnetic textures that can be easily modified, our magnonic hardware architecture is reprogrammable, unlike most present-day information-processing architectures. Using this new architecture, we design the simplest magnonic component, a spin-wave diode that admits only the unidirectional propagation of spin waves. We find that the bound spin-wave states in a domain wall become chiral and are spatially separated depending on their propagation direction, which enables us to realize the diode effect for spin-wave transport along domain walls. Furthermore, we demonstrate that the function of the spin-wave diode is easily altered from forward transmitting to reverse transmitting by simply moving domain walls via current-induced spin-transfer torque.

Our magnonic architecture opens up new pathways for realizing an evolvable pure spin-wave computer.

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Vol. 5, Iss. 4 — October - December 2015

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Figure 1
The domain-wall circuit and EASA circuit. (a) Upper diagram: simulated EASA-induced surface spin-wave mode propagating along a U-shaped path decorated by EASA. Lower diagram: Simulated spin-wave interconnection from an EASA wire to a domain-wall wire. Both images are simulated on a homogeneous magnetic wafer of size $1600 nm \times 1600 nm \times 150 nm$ with spin-wave excitation at the position indicated by the triangle. Inset: The dispersion relation for the bulk spin wave (black), EASA surface mode (blue), and domain-wall bound state (red); the excitation frequency is indicated by the dashed line lying below the bulk gap and above the surface-wave gap. (b) Simulated spin-wave propagation in a domain-wall circuit made of the domain-wall wires printed on a magnetic wafer with a biaxial anisotropy and four possible domain orientations, and wafer size $2000 nm \times 2000 nm \times 10 nm$ . (c) Simulated EASA-induced surface spin wave transporting through an EASA circuit in a homogeneous magnetic wafer of size $2000 nm \times 2000 nm \times 30 nm$ .
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Figure 2
The design of the diode and the simulations. Top row: The design of the spin-wave diode. (a) Domain-wall wire without DMI. The bound spin-wave state propagates in both directions identically, where the domain-wall region is shaded with darker brown color and is pinned at the kink position. (b) Domain-wall wire with DMI. The bound states propagating upward or downward are spatially shifted to the right or left side of the wall. (c) Spin-wave diode—forward direction. The spin wave transmits from the upper to the lower terminal. (d) Spin-wave diode—reverse direction. The spin wave is blocked from the lower to the upper terminal. The wavy lines denote the route of the spin-wave propagation. Bottom row: Numerical micromagnetic simulations of the spin-wave diode (color map of $m_{z}$ ). (e) Without DMI, the bound spin-wave state travels symmetrically. (f) With DMI, the bound spin-wave states become chiral. (g) Spin-wave diode—the forward direction. (h) Spin-wave diode—the reverse direction. In all panels, the little green bar indicates the spin-wave injection location where an oscillating magnetic field is applied.
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Figure 3
The spatial profile for the effective scalar potential and the effective magnetic field. We show the spatial distribution of the scalar potential $V (z)$ and the magnetic field $B (z)$ in the $y − z$ plane. The density map is the scalar potential, and the disk size represents the magnitude of the magnetic field pointing in the $x$ direction.
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Figure 4
Reprogramming the diode by changing the sign of the DMI parameter. The forward direction of the spin-wave diode for $D < 0$ is opposite to that for $D > 0$ in Figs. 2 and 2. The insets on the top right are the spin-wave propagation diagrams.
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Figure 5
Reprogramming the diode by moving the domain-wall position. The functionality is tuned by the domain-wall position (from position 1 to 5, the domain-wall center is indicated by the dashed line). The spin wave is injected from the left (right) terminal for the upper (lower) row. (a) Position 1, off in both directions. (b) Position 2, diode with the forward direction from right to left. (c) Position 3, on in both directions. (d) Position 4, diode with the forward direction from left to right, opposite to position 2. (e) Position 5, off in both directions, similar to position 1. The kinks are to pin the domain walls. The simulation is performed on a two-dimensional film of size $1600 nm \times 1600 nm$ with an additional perpendicular anisotropy in the terminal area to mimic the EASA in three-dimensional samples. (See the movie in Ref. [24] for simulated real-time switching among these functions by current-induced domain-wall motion.)
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Physical Review X

Spin-Wave Diode

Jin Lan (兰金), Weichao Yu (余伟超), Ruqian Wu, and Jiang Xiao (萧江)

Phys. Rev. X 5, 041049 – Published 28 December 2015

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