We discuss elementary topological defects in soft magnetic nanoparticles in the thin-film geometry. In the limit dominated by magnetostatic forces the low-energy defects are vortices (winding number n = +1), cross ties (n = -1), and edge defects with n = -1/2. We obtain topological constraints on the possible composition of domain walls. The simplest domain wall in this regime is composed of two -1/2 edge defects and a vortex, in accordance with observations and numerics.
@article{arxiv.cond-mat/0508740,
title = {Topological defects in flat nanomagnets: the magnetostatic limit},
author = {G. -W. Chern and H. Youk and O. Tchernyshyov},
journal= {arXiv preprint arXiv:cond-mat/0508740},
year = {2007}
}