Parameters of the antidot system

Since three-dimensional arrays of objects become rapidly impractical to simulate even across modern supercomputing clusters, a feasibility study was conducted to assess the limits of the available hardware when computing the hysteresis loops for these systems.

A set of different self-assembled experimental samples were prepared from nickel, iron, cobalt and Ni$_{50}$Fe$_{50}$ permalloy from spheres sized 20nm $\leq d \leq$ 1000nm. For the initial micromagnetic study we chose to model the nickel sample. Nickel has a relatively large exchange length ( $\lambda_{\mathrm{ex}}\approx7.5$nm) when compared to Ni$_{50}$Fe$_{50}$ permalloy ( $\lambda_{\mathrm{ex}}\approx2.75$nm), allowing for physically larger systems to be computed within a simulation domain of a comparable discrete cell count.

For the simulations, the parameters for amorphous nickel were selected ($M_s =$ 4.93$\times$10$^5$ A/m, $A =$ 8.5$\times$10$^{-12}$ J/m, $K_1 =$ 0 J/m$^3$) and to improve convergence a damping constant $\alpha$ of 0.25 was chosen.