yWe develop a semi-empirical many-body interatomic potential suitable for large scale molecular dynamics simulations of magnetic a-iron. The functional form of the embedding part of the potential is derived using a combination of the Stoner and the Ginzburg-Landau models. We show that it is the symmetry broken solutions of the Ginzburg-Landau model describing spontaneous magnetization of atoms that provide the link between magnetism and interatomic forces. We discuss a range of potential applications of the new method.