Spin-torque vortex-oscillator with modified saturation magnetization in ferromagnetic nanodots

Abstract

Recent years have seen greater interest in manipulating vortex states in magnetic nanostructures for non-volatile memory and logic networks. We show how reducing saturation magnetization locally in ferromagnetic thick nanodot vortex-based spin-torque nano-oscillators modulates their frequency using micromagnetic simulations. When a spin-polarized current and a static in-plane magnetic field are applied to the vortex core of an isolated thick nanodot, the uniform gyrotropic modes and the first higher-order gyrotropic mode resonate at different frequencies in various saturation magnetization areas. The intensity of the first higher-order mode gets almost suppressed in areas with modified saturation magnetization. With linewidths ranging from 25 to 70 MHz with the considered dimensions, these small spin-torque vortex-oscillator devices made of thick Permalloy nanodots seem promising for use in gigahertz signal processing. Our study suggests that locally modifying saturation magnetization may be a cost-effective technique to build dense oscillator and array networks for neuromorphic computing without lithographical fabrication stages.