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

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.

14 pages and 5 figures; published version

References in corpus (5)

• Artificial "spin ice" in a geometrically frustrated lattice of nanoscale ferromagnetic islands
• Artificial square ice and related dipolar nanoarrays
• Magnetic monopole and string excitations in a two-dimensional spin ice
• Vertex dynamics in finite two dimensional square spin ices
• Nambu monopoles interacting with lattice defects in two-dimensional artificial square spin ice

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• Gauge-Free Duality in Pure Square Spin Ice: Topological Currents and Monopoles
• Controlling degeneracy and magnetization switching in an artificial spin ice system of peanut-shaped nanomagnets