Short spin waves excitation in spin Hall nano-oscillators

Abstract

This study investigates the excitation of short-wavelength spin waves (SWs) in nanowire-based spin-Hall nano-oscillators (SHNOs). Using micromagnetic simulations, we study the wavelength of propagating SWs as a function of nanowire width, ranging from 10 to 50 nm, excited in a 1.7 nm-thick CoFeB layer using a pure spin current generated by a 5 nm thin platinum layer via the spin Hall effect. Our results showed that SWs with shorter wavelengths are excited in narrow widths at higher magnetic fields and higher currents. In addition, the wavelength of the propagating waves scales linearly with the width of the nanowire. We attribute the emission of short wavelength due to the quantization of SWs in the nanowire. By reducing the nanowire width, SWs with ultrashort wavelengths are excited at high frequencies, with larger propagation speeds and longer attenuation lengths. Our results show that ultrashort SWs with wavelengths as short as 80 nm can be generated in metallic-based SHNOs, with a group velocity of vg = 1.6 µm/ns and attenuation length of Latt = 0.6 µm. These findings have significant implications for the scalability of magnonic devices, which could have potential applications in SW-based logic and neuromorphic computing. © 2023 Elsevier B.V.