Optimizing Hybrid Ferromagnetic Metal-Ferrimagnetic Insulator Spin-Hall Nano-Oscillators: A Micromagnetic Study

TL;DR

This study uses micromagnetic simulations to explore how material properties of a ferrimagnetic insulator influence the performance of hybrid spin-Hall nano-oscillators, aiming to optimize their microwave output for spintronic applications.

Contribution

It provides a detailed analysis of how LAFO parameters affect the magnetic dynamics and output power of hybrid SHNOs, offering design guidance for targeted spin excitation characteristics.

Findings

Auto-oscillation threshold current is weakly dependent on LAFO parameters.

Output power varies nonlinearly with saturation magnetization and anisotropy.

A critical anisotropy value triggers propagating spin-waves.

Abstract

Spin-Hall nano-oscillators (SHNO) are nanoscale spintronic devices that generate high-frequency (GHz) microwave signals useful for various applications such as neuromorphic computing and creating Ising systems. Recent research demonstrated that hybrid SHNOs consisting of a ferromagnetic metal (permalloy) and lithium aluminum ferrite (LAFO), a ferrimagnetic insulator, thin films have advantages in having lower auto-oscillation threshold currents ($I_{\text{th}}$) and generating larger microwave output power, making this hybrid structure an attractive candidate for spintronic applications. It is essential to understand how the tunable material properties of LAFO, e.g., its thickness, perpendicular magnetic anisotropy ($K_u$), and saturation magnetization ($M_s$), affect magnetic dynamics in hybrid SHNOs. We investigate the change in $I_{\text{th}}$ and the output power of the device as the LAFO parameters vary. We find the $I_{\text{th}}$ does not depend strongly on these parameters, but the output power has a highly nonlinear dependence on $M_s$ and $K_u$. We further investigate the nature of the excited spin-wave modes as a function of $K_u$ and determine a critical value of $K_u$ above which propagating spin-waves are excited. Our simulation results provide a roadmap for designing hybrid SHNOs to achieve targeted spin excitation characteristics.