Magnetic dynamic properties of Fe nanorings with small defects were simulated with Monte Carlo method. It is found that hysteresis loops of small defect Fe nanoring have "bistable" characteristics, which is consistent with experimental results. Energy research shows that vortex states appear in the region of local energy minimum. Remanence of defect system changes with defect location: The remanence increases first and then decreases with the increase of Y, and remains relatively stable in the middle region. Spin configuration of the system explains the above phenomenon well.

With Monte Carlo simulation,we study magnetic properties and controllable vortex circulation of asymmetric Co nanorings.Simulated results indicate that magnetic field direction has great effect on magnetic states and magnetization process of asymmetric Co nanorings.It is found that direction of the magnetic-moment circulation in asymmetric nanorings can be controlled by gradient of the domain-wall energy along the circumference in cooperation with an external magnetic field.It is found that size effect is obvious on stability of vortex-type state and magnetization process of asymmetric nanorings.