Magnetic properties for cobalt nanorings: Monte Carlo simulation

In this paper, two structure models of cobalt nanoring cells (double-nanorings and four-nanorings, named as D-rings and F-rings, respectively) have been considered. Base on Monte Carlo simulation, the magnetic properties of the D-rings and F-rings, such as hysteresis loops, spin configuration, coercivity, etc., have been studied. The simulated results indicate that both D-rings and F-rings with different inner radius (r) and separation of ring centers (d) display interesting magnetization behavior and spin configurations (onion-, vortex- and crescent shape vortex-type states) in magnetization process. Moreover, it is found that the overlap between the nearest single nanorings connect can result in the deviation of the vortex-type states in the connected regions. Therefore, the appropriate d should be well considered in the design of nanoring device. The simulated results can be explained by the competition between exchange energy and dipolar energy in Co nanorings system. Furthermore, it is found that the simulated temperature dependence of the coercivity for the D-rings with different d can be well described by H_c=H₀ exp−(T/T₀)^p].