Dipolar induced magnetic anisotropy and magnetic topological defects in ultrathin films - art. no. 104409

A Taylor expansion of the spin field enables us to obtain a local represent ation of dipole-dipole interactions in the plane. The magnetic anisotropy i nduced by the lattice symmetry by means of the dipolar interaction is analy zed for a hexagonal lattice. The reduction of the divergence of higher term s of the dipolar Hamiltonian lends to a set of nonlinear equations on the p artial derivatives of the spin field. Topological defects are shown to be a pproximate solutions of these equations and are classified according to the ir validity and occurrence frequency. Because of dipolar interactions, this result is shown to be general for two-dimensional lattices observed on a l arge scale.