Magnetic random access memory (MRAM) would combine the benefits of the hard drive (non-volatile, cheap, high density of bits) with the benefits of RAM (fast, mechanically robust). One proposal for MRAM involves the vortex state of nanorings, a state in which the magnetic moments align circumferentially in the clockwise or counterclockwise direction. For a symmetric ring in a uniform field, these states are energetically degenerate and cannot be selected experimentally. A circular field allows us to study the switching behavior between these vortex states. We have developed an experimental technique to apply a local circular field by passing current through the tip of an atomic force microscope. I will discuss how the atomic force microscope works, our experimental results demonstrating switching between the vortex states, and our understanding of the evolution of these states based on our simulations. We predict novel states that arise from both energy minimiza!
tion and topological constraints.
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