Study of String-Like Excitations in Artificial Spin Ice Through Linear Chains of Magnetic Dipoles

In this work we study a system of classical magnetic Ising-like dipoles (spins) on the square lattice interacting exclusively by magnetic dipolar interaction. The spins are positioned in sequence, forming linear chains on the lattices links (strings), parallel to its plane. These strings are constructed by Self-Avoiding Walks (SAW's). For each string length, we generate all reachable microstate the system in order to make the accurate analysis of the system through the canonical ensemble. Our purpose is to better understand the behavior of excitation type strings in artificial spin ice, since the studied chains are similar to those excitations, which present as remarkable feature the presence of magnetic monopole quasi-particles associated to its extremes. The studied system is similar to the homopolymers in network-based SAW's. We observed signs of phase transition which are analyzed by such quantities as the end-to-end distance and the radius of gyration. Among the phase transition signs observed, the compact-extended transition of strings is well identified, such as the $\theta$-transition of homopolymers. We also present some results for the hexagonal lattice. We observed that the low temperature properties of the square lattice are determined by configurations that satisfy a rule of alternation in the direction of the walk, while in the hexagonal lattice the minimum end-to-end distance is the key factor.

Thanks financial support: CNPq e FAPEMIG.