Numerical quadratic energy minimization bound to convex constraints in thin-film micromagnetics

We analyze the reduced model for thin-film devices in stationary micromagnetics proposed in DeSimone et?al. (R Soc Lond Proc Ser A Math Phys Eng Sci 457(2016):2983?C2991, 2001). We introduce an appropriate functional analytic framework and prove well-posedness of the model in that setting. The scheme for the numerical approximation of solutions consists of two ingredients: The energy space is discretized in a conforming way using Raviart?CThomas finite elements; the non-linear but convex side constraint is treated with a penalty method. This strategy yields a convergent sequence of approximations as discretization and penalty parameter vanish. The proof generalizes to a large class of minimization problems and is of interest beyond the scope of thin-film micromagnetics.