Spin defect motion at interfaces of spin domains in buckled colloidal crystals

Geometric frustration appears in systems ranging from glasses to spin liquids, with the antiferromagnetic Ising model on a triangular lattice serving as a classic example. We study a colloidal analog to the Ising model, where hard spheres confined in a gap of ~1.5 particle diameters buckle up and down, like Ising spins, and arrange themselves into distinct spin patterns to maximize free volume. The base unit of these patterns is the motif: the set of adjacent spins belonging to a particle and its nearest neighbors. Our system exhibits spin domains composed of "lines" or "kinks", the two motifs that pack most efficiently. Ordered line-and-kink spin domains composed of adjacent rows of alternating spin particles are separated by disordered interfaces composed of less efficiently-packed motifs. We observe that spin defects proliferate and move in the domain interfaces, which may play an important role in the coarsening of adjacent mismatched spin domains. We investigate the role of spin motifs in directing spin defect propagation during domain coarsening. Understanding the allowed motions of spin defects could ultimately enable better models of how spin domains grow and merge in buckled colloidal crystals and other geometrically frustrated systems.