From confinement to deconfinement of magnetic monopoles in artificial rectangular spin ices

TL;DR

This paper investigates how the geometric ratio in artificial rectangular spin ices influences magnetic monopole behavior, revealing conditions for monopole deconfinement and anisotropic properties.

Contribution

It demonstrates that adjusting the lattice ratio $ ext{a/b}$ can stabilize the ice regime and enable monopole deconfinement in artificial rectangular spin ices.

Findings

Monopoles become deconfined at $ ext{a/b} oughly ext{sqrt}(3)$.

System exhibits high anisotropy with near-zero string tension along specific directions.

Ground state transitions and thermodynamic properties are characterized.

Abstract

We study a frustrated two-dimensional array of dipoles forming an artificial rectangular spin ice with horizontal and vertical lattice parameters given by $a$ and $b$ respectively. We show that the ice regime could be stabilized by appropriate choices for the ratio $\gamma \equiv a/b$. Our results show that for $\gamma \approx \sqrt{3}$, i.e., when the center of the islands form a triangular lattice, the ground state becomes degenerate. Therefore, while the magnetic charges (monopoles) are excitations connected by an energetic string for general rectangular lattices (including the particular case of a square lattice), they are practically free to move for a special rectangular lattice with $\gamma \approx \sqrt{3}$. Besides that, our results show that for $\gamma > \sqrt{3}$ the system is highly anisotropic in such a way that, even for this range out of the ice regime, the string tension almost vanishes along a particular direction of the array. We also discuss the ground state transition and some thermodynamic properties of the system.