Frequency Tunability of Spin-Torque Vortex Oscillator in Permalloy Nanodisks with Modified Material Properties

The manipulation of the vortex state in magnetic nanostructures has received a lot of interest in recent decades, with potential applications in nonvolatile magnetic random-access memory and logic networks. For wireless communication advancements, nano-sized, and low-phase-noise, adjustable transmitter-receiver networks are critical. Herein, it is shown that by using micromagnetic simulations when the saturation magnetization is reduced in a particular region of a magnetic nanodisk, the frequency tunability in such disks can be achieved. The gyrotropic mode of the vortex core is excited with spin-polarized current and an in-plane static magnetic field and found that an isolated magnetic vortex shows different resonance frequencies at different saturation magnetization regions. The dynamics of the mutual synchronization between two such dipolarly coupled magnetic vortices are numerically investigated, and the essential distances at which synchronization occurs are also identified. These incredibly small vortex-based oscillator devices have linewidths of the order of 40-60 MHz, making them prospective candidates for signal-processing applications and a strong new tool for basic research on vortex dynamics in magnetic nanostructures.