5.2.1 Experimental results

Figure 5.6: Measured coercivity of different samples plotted versus the inverse of the interantidot distance (extracted from the Ph. D. thesis of J.M. Torres [Torres 05]).

The coercivity of series of Fe antidot arrays was studied by J. M. Torres [Torres 05]. The arrays were produced by using X-ray lithography on a $ 30 nm$ thick Fe(001)/GaAs film grown by Molecular Beam Epitaxy in the group of Prof. J.A.C. Bland in the Cavendish Laboratory (Cambridge). The lithographed region covered a $ 0.8\
mm \times 0.8 mm$ area out of a $ 2 mm \times 2 mm$ film. The samples prepared had the following set of diameters and separation (D,$ \lambda $): ($ 2 \mu m$, $ 2 \mu m$), ($ 1 \mu m$, $ 1 \mu m$), ($ 2 \mu m$, $ 0.2 \mu m$) and ($ 1 \mu m$, $ 0.1 \mu m$). The coercivity was measured in the easy axis and hard axis configurations using an alternating gradient field magnetometer (AGFM) in the Instituto de Ciencia de Materiales de Aragón. The samples presented two jump in the hysteresis loops in both configurations: the first jump had a very similar value to that of the samples before the lithography procedure. This jump corresponds to the switching of the non-lithographed area. The second jump corresponds to the interantidot area. That later jump value can be several times higher than the former. This fact can be assigned to the stabilizing role of the antidots. Both processes can not be considered ``a priori'' independent, since the switching of the antidot region can be caused by the external region. As expected, the obtained coercivities in easy axis configuration are larger than the hard axis ones. Plotting the value of this second jump as a function of $ \lambda $ a hypothesis of the linear dependence with the inverse of $ \lambda $ was suggested (see Fig. 5.6) [Ruiz-Feal 02]. From that, the coercivity was supposed to follow a simple scaling law with the inverse of $ \lambda $. Generally speaking, the geometrical parameters $ \lambda $ and $ D$ of every sample were different, and, therefore, the coercivity can not be plotted as a variation of a single parameter. Nevertheless, there is a increase of the coercivity with the reduction of the distance $ \lambda $, but this dependence can be more complex than the one shown in Fig. 5.6. More ample series of sample are needed in order to verify the scaling law. Series in which one of the parameters is kept constant are specially interesting.