  Magnetic skyrmions are topologically protected stable magnetization
configurations, which are expected to be a promising candidate as information
carrier, while defect is inevitable and plays an important role on the
stabilization and movement of skyrmion. In this paper, we investigated the
influence of a point defect and a ring defect on the stabilization and dynamics
of skyrmion in the nanodisk, where the defect are acquired by local
modification magnetic material parameters. Considering the combined action of
geometry confinement and pinning effect, we demonstrate the preferred skyrmion
position as a function of defect type and distance between skyrmion and a point
defect. We also show the confinement effect on skyrmion size in the presence of
a ring defect due to circular symmetry. Finally, in the application of spin
transfer nano-oscillator, we show that the skyrmion can be pinned or rotate in
the nanodisk, the oscillator frequency can be modified in a large variation by
the ring defect. These findings provide a complete understanding of interaction
between skyrmion and defect in the confined geometry and may provide a good
strategy for the design of skyrmion oscillators.
