5.2.3 Damaged zone simulations

Figure: (a) Simulated hysteresis loops corresponding to antidots film with a region of width $ r=100 nm$ of reduced anisotropy and antidot diameter $ D = 1000 nm$ for different separations $ \lambda $ and (b) simulated coercive force dependence of the interantidot distance $ \lambda $ for the same system.

(a) (b)
There are several reasons for the disagreement between the simulations and the experiments regarding the sizes where the non trivial dependence of the coercivity appears. The magnetic parameters, $ A$- exchange constant, $ K$- magnetic anisotropy or $ M_s$- saturation magnetization, that determine the magnetic processes and the characteristic lengths can be different to that considered in the simulations. The characteristic lengths determine the size of the minimizing structures and from that point of view, these lengths could be larger in the experiment that the obtained from the values used in the simulations. The reason for this fact can be that in reality the film may be polycrystalline instead of a single crystal structure.

Additionally, the X ray lithography can damage the structure of the region surrounding the antidots. This fact would effectively reduce the interantidot distance extending the zone where the coercivity presents appreciable variation. We will suppose, in the simulations of this section, that there is a region around the antidots of width $ r=100 nm$ in which the magnetic anisotropy values equal to zero. Due to the large in-plane anisotropy of the Fe film, we consider a 2D model. Periodic boundary conditions are applied in order to model a large array. The intrinsic parameters of the Fe film are the same used in the previous chapter. The discretization length is $ 4 nm$ that is less than the exchange correlation length. The antidot diameter is $ 1 \mu m$ and different separations $ \lambda $ are considered. The obtained coercivity for the easy axis configuration adding the damaged region is independent of $ \lambda $ in a broad range of separations $ \lambda $ (see Fig. 5.9). This indicates that the considered interantidot distances range corresponds to the diluted regime of the antidots.