Deterministic switching of antiferromagnetic spin textures by nonlinear magnons

Introduction

Topological spin textures such as magnetic skyrmions^{1, 2, 3, 4, 5, 6–7} are promising candidates as information carriers for next-generation memory-in-logic devices⁸. Antiferromagnetic spin textures^{9, 10, 11, 12–13}, compared to their ferromagnetic counterparts, innately possess high stability with respect to external disturbance^14,15 and high-frequency dynamics^{16, 17, 18–19} compatible with ultrafast information processing. Collective spin dynamics in a magnetically ordered system known as spin waves (or magnons)²⁰, are promising for low-power information processing due to its inherent advantage of charge-free transport. Nonlinear dynamic systems have been studied to a wide variety of scientific disciplines in physics, biology and engineering, including turbulent fluids, neural networks and Josephson arrays, etc²¹. Nonlinear spin waves are spin waves with large amplitudes that exhibit various nonlinear effects, such as the frequency multiplication²² and the foldover effect²³. Driving nonlinear spin-wave excitations in a non-uniform spin texture (k₀ ≠ 0) using uniform microwave perturbation ($k_1\approx 0$, namely, $k_1\ll 1$ rad μm^-1) is inefficient^{4, 5, 6–7}. Likewise, the excitation of short-wavelength magnons^24,25 ($k_1\ne 0$, specifically, $k_1>1$ rad μm^-1) in uniform spin alignment ($k_0=0$), is again proved to be highly challenging and usually inefficient. One would need to exert non-uniform excitation field ($k_1\ne 0$) on a static spin texture ($k_0\ne 0$) in the condition $k_1\approx k_0\ne 0$ in order to increase the excitation efficiency and reduce the threshold for nonlinear behaviors. In view of other prerequisites for deeply nonlinear behaviors in noncollinear textures, it is extremely hard to find a ferromagnetic system that simultaneously hosts spin textures⁸ and possesses low damping^26,27, particularly at room temperature^1,2. However, a recently revisited antiferromagnet (AFM), α-Fe₂O₃, also known as hematite, may provide an exceptional opportunity to study nonlinear magnons, since it has been proved to exhibit ultralow magnetic damping^{28, 29–30} of ${10}^{-5}$ and to host noncollinear AFM textures such as half-skyrmions and bimerons at room temperature in thin films¹².

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