Strain-tunable magnetic vortex oscillators

• Applicant: Vadym Iurchuk, Ph.D.
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501377640

The ground state of nanoscale circular magnetic disks of certain geometric aspect ratios is a spontaneously forming stable vortex configuration with circulating in-plane magnetization and a vortex core pointing out-of-plane. Resonantly exciting the vortex core via either an rf magnetic field or an rf spin-polarized current yields a gyrotropic motion around its equilibrium position, characterised by a specific eigen-frequency, which depends on the material parameters and the disk geometry. Such oscillations, which can be read out via periodic magnetoresistance changes, generate rf signals with high quality factors (>10000) in the sub-GHz bandwidth. While all these features make vortex-based nano-oscillators interesting as nanoscale rf sources, the major drawback remains their low frequency tunability associated with the linear characteristics of the gyrotropic mode. In this project, we propose to investigate (experimentally and by micromagnetic simulations) the role of magnetostriction in improving the tunability of vortex nano-oscillators. To tackle the defined goal, the proposed study is divided into three main parts. First, we will study the strain-induced shift of the vortex core gyration eigen-frequency and corresponding modification of the gyration trajectory in magnetostrictive ferromagnetic disks grown on piezoelectric substrate. Here, we will evaluate the magnetoelastic anisotropy contribution to the vortex core dynamics depending on the sign of the magnetostriction constant and the presence of the magnetocrystalline anisotropy in magnetic disks. In the next part, we will study the interplay between the strain-induced magnetoelastic anisotropy and the interlayer magnetostatic interaction in stacked double-vortex structures and their impact on the eigen-frequency splitting. In the last part of the proposed study, we will investigate the vortex formation in ferrimagnetic micro-disks near angular momentum compensation point. Subsequently, the strain-induced modification of the resonant dynamics of the ferrimagnetic vortices and the corresponding frequency tunability will be evaluated as a function of the material parameters and geometry of the structures. These findings are expected to expand the current knowledge on the strain-controlled magnetization dynamics in confined magnetic structures.

• DFG Programme: Research Grants