Magnetic Frustration in Circular Arrays of Dipoles

Magnetostatically interacting structures consisting of 1.5 μm diameter rings of radially oriented nanomagnets were investigated using magnetic force microscopy. An even number of nanomagnets, 16 in this case, formed a ground state in which the magnetizations of neighboring nanomagnets were oriented antiparallel. However, an odd number of nanomagnets, 15, led to a frustrated state in which at least one pair of neighboring nanomagnets was magnetized parallel, giving a net radial magnetic charge. The “defect” in the structure was moved around the ring by a modest external field.