Large amplitude oscillations (switching) of bi-stable vortex structures in zero field

A ferromagnetic block (2a×2b×2c) with three unequal axes supports a vortex structure that intersects each of the two opposite surfaces of largest area. Swirls appear at points (xp, yp, c) and (?xp, yp, ?c) in state-A. In state-B the swirls are at points (?xp, ?yp, c) and (xp, ?yp, ?c). With micromagnetic simulations we demonstrate the possibility of a nucleation-free switching between those states, with possible applicability in devices. The oscillations are accompanied by large external fields from the magnetic charge at the core of the intersections of the vortices with the surface. These fields of the order of a quarter of the saturation inductance move over a distance 2xp～c in fractions of a ns.