Controllable switch of magnetic vortices in polyhedral iron nanoflakes

The discovery of magnetism in ultrathin crystals opens up opportunities for exploring new states of matter and developing next-generation spintronic devices. It is thus crucial to carry out a thorough understanding of microscopic magnetic properties in ultrathin crystals. Here, we systematically investigate magnetic properties in chemical-vapor-deposition-grown iron nanoflakes via in situ Lorentz transmission electron microscopy and magnetic force microscopy. Our results reveal robust room-temperature ferromagnetism with vortex ground states, compared with conventional domain walls, in samples of polyhedral shapes. We further demonstrate that these vortices can be switched in a controllable manner with an external magnetic field. Micromagnetic simulations suggest that these behaviors can be explained by the competition among Heisenberg exchange, anisotropy, and demagnetizing energies. These findings provide guidelines for the design of magnetic and spintronic devices using ultrathin magnetic crystals.