F. S. Nascimento, L. A. S. Mól, W. A. Moura-Melo, A. R. Pereira
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 $a/b$. Indeed, for special values of $\gamma \equiv a/b$, 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 free to move for a special rectangular lattice with $a/b\approx 1.735$ or 0.556. We also discuss the ground state transition and some thermodynamic properties of the system.
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http://arxiv.org/abs/1208.5765
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