A ferromagnetic skyrmion-based nano-oscillator with modified profile of Dzyaloshinskii-Moriya interaction

Magnetic skyrmions have attracted great interest in recent years due to their potential wide-scale applications in spintronic devices, such as the spin torque nano-oscillator (STNO) and racetrack memory. The spin-transfer torque can drive the motion of skyrmions on a ferromagnetic nanodisk, where skyrmions are stabilized by the Dzyaloshinskii-Moriya interaction (DMI). However, the Magnus force acted on a skyrmion can drive the skyrmion moving toward either the nanodisk center or edge, which may lead to the destruction of skyrmion at edge, and thus reduce the performance of skyrmion-based STNO. In order to overcome this problem, we designed a ferromagnet/spacer/ferromagnet/heavy metal STNO model, in which the inner and outer areas of the ferromagnetic nanodisk have different DMI, and those skyrmions could move along the boundary between inner and outer areas. We investigated the dynamics of skyrmions in such a STNO model by adjusting several geometrical and material parameters. We obtained an optimal frequency of skyrmion oscillation of 3.43 GHz. Our results may be useful for designing future STNOs based on skyrmions, where the Magnus-force-induced destruction of skyrmions can be effectively avoided.