Generating microwaves with antiferromagnetic skyrmions

Magnetic moments inside current-driven magnetic devices create phenomena such as vortices and various patterns of flow. The design of nano-oscillators that generate microwave signals requires an understanding of these spin dynamics.

Skyrmions are swirling configurations of magnetic moments that create a reversal of the spins around them. Skyrmions are topographically protected, so they are stable during the motion driven by spin torques. Their ability to stay in a local area means they could lead to small magnetic devices. However, ferromagnetic skyrmion-based spin-torque nano-oscillators have been limited by their inability to reach high oscillation frequencies.

Shen et al. utilize micromagnetic simulations to support the proposition that through the use of skyrmions with spins that are antiferromagnetic instead of ferromagnetic, one could achieve spin torque nano-oscillators that can produce frequencies up to tens of GHz. The antiferromagnetism also eliminates problematic stray magnetic fields. To further understand the dynamics of the spin textures involved, the researchers also modeled a nanodisk device to compare the behavior in ferromagnetic and antiferromagnetic skyrmions. They pointed out that combining multiple skyrmions in the same device creates even higher frequency microwave signals and enables greater frequency control.

By studying the dynamics in these microscopic magnetic regions in relation to speed and signal generation, the authors hope to aid the design of more efficient microwave devices.

Source: “Spin torque nano-oscillators based on antiferromagnetic skyrmions,” by Laichuan Shen, Jing Xia, Guoping Zhao, Xichao Zhang, Motohiko Ezawa, Oleg A. Tretiakov, Xiaoxi Liu, and Yan Zhou, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5080302 .