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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.

Richard Boardman 2006-11-28