Optimizing hybrid ferromagnetic metal–ferrimagnetic insulator spin-Hall nano-oscillators: A micromagnetic study

Spin-Hall nano-oscillators (SHNOs) 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 ferrite-based (LAFO) insulating ferrimagnetic thin films have advantages in having lower auto-oscillation threshold currents (Ith) 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 (Ku,LAFO), and saturation magnetization (Ms,LAFO), affect magnetic dynamics in hybrid SHNOs. We investigate the change in Ith and the output power of the device as the LAFO parameters vary. We find the Ith does not depend strongly on these parameters, but the output power has a highly nonlinear dependence on Ms,LAFO and Ku,LAFO. We further investigate the nature of the excited spin-wave modes as a function of Ku,LAFO and determine a critical value of Ku,LAFO above which propagating spin-waves are excited. Our simulation results provide a roadmap for designing hybrid SHNOs to achieve targeted spin excitation characteristics.