Soft magnetic permalloy films with uniaxial in-plane anisotropy are widely used as magnetic sensors. The magnetic properties of such films are described by the ripple theory instead of the Stoner-Wohlfarth theory. The ripple theory includes the influence of local anisotropies, which lead to intrinsic demagnetizing fields. In ferromagnetic nanostructures strong demagnetizing fields arise from magnetic divergences at the surface of the structure. These fields dominate the magnetization in the structures and the magnetization reversal in applied fields.