Dynamics of hybrid skyrmions with different helicities in synthetic antiferromagnetic nanodisks

Abstract As a new type of microwave signal generator, spin-torque nano-oscillators (STNOs) based on skyrmions have potential application value. In recent years, hybrid skyrmions with arbitrary helicity have been proposed in chiral materials. In this paper, we have investigated the dynamics of self-sustained oscillation of magnetic hybrid skyrmions in nanodisks with synthetic antiferromagnetic (SAF) multilayer structure, which can effectively eliminate the Hall effect of skyrmions and ensure their stable circular motion. We have found that the smaller the helicity of hybrid skyrmions, the smaller the radius of their motion trajectory, the faster the velocity of their stable motion, and the higher the frequency of STNOs. Furthermore, the smaller the helicity, the larger the upper threshold of current density, and a higher upper threshold of current density allows us to regulate the frequency to higher values and improve the performance of STNOs. We have developed the force expressions of hybrid skyrmions in the free layers of SAF structure utilizing the Thiele equation, and revealed the mechanism of hybrid skyrmions with different helicities in circular motion with different trajectory radii through force analysis in both tangential and radial directions. This work is beneficial for designing and developing the next generation of spin nano-oscillators based on hybrid skyrmions.