A Computational Micromagnetic Study of Controlling Vortex Chirality in Ferromagnetic Nanorings



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As we decrease the dimensions of a ferromagnetic material to the nanoscale, novel magnetic phenomena - unseen in macroscopic materials - result. Thin ferromagnetic nanorings exhibit especially unique magnetic states, including the vortex state in which the magnetic moments align circumferentially, leaving no stray magnetic fields. These magnetic configurations have potential applications for a new type of nonvolatile computer memory, in which bit information is encoded in the clockwise or counterclockwise chirality of the vortex state. Control over vortex chirality has been experimentally challenging. Previous experiments have applied a uniform in-plane field to control the magnetic configuration. In asymmetric rings, one can exploit the non-uniform geometry to control the direction of domain wall movement, and hence the final chirality of the magnetic state. However, in symmetric rings, an in-plane field cannot directly control the chirality of the ring. Through a series of micromagnetic simulations, we investigate a novel method of controlling the magnetic state, in which we apply a circular magnetic field as if by an infinite current carrying wire. The corresponding chirality of the ring is determined by the polarity of the current. We observe transition states that contain two or more 360 degree domain walls. These states occur at lower applied currents and promise lower power requirements for technological applications. Preliminary results show that these states are stable at room temperature.



Nanorings, Simulations