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, - exchange constant, - magnetic anisotropy or - 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.
(a) Simulated hysteresis loops corresponding to antidots film with a
region of width
of reduced anisotropy and antidot diameter for different
and (b) simulated coercive force dependence of the interantidot
distance for the
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 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 that is less than the exchange correlation
length. The antidot diameter is and different separations are considered. The
obtained coercivity for the easy axis configuration adding the damaged
region is independent of
in a broad range of separations (see Fig. 5.9).
This indicates that the considered interantidot distances range
corresponds to the diluted regime of the antidots.