Magnetic Frustration in Circular Arrays of Dipoles

Abstract

Magnetostatically interacting structures consisting of 1.5 mu m 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.