This event is open to current Amherst College students, faculty and staff (Amherst College ID required).
When the size of a ferromagnetic structure is on the order of a single domain, where all magnetic moments align parallel to one another, fascinating physics can result. Circularly symmetric structures (i.e., disks and rings) can support a “vortex” state in which the moments align circumferentially with a clockwise or counterclockwise circulation. Typical experiments that apply in-plane magnetic fields cannot select between the CW and CCW states. Instead, we locally pass current through the tip of an atomic force microscope to apply a circular field, directly controlling the vortex circulation. Magnetic force microscopy allows us to image the resulting states in disks and rings. Simulations predict novel states with multiple 360-degree domain walls in rings, which we can understand by considering the switching process and the topology of the domain walls. Potential applications in data storage will be discussed.