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Artificial ‘spin ice’ in a geometrically frustrated lattice of nanoscale ferromagnetic islands

An Addendum to this article was published on 01 March 2007

Abstract

Frustration, defined as a competition between interactions such that not all of them can be satisfied, is important in systems ranging from neural networks to structural glasses. Geometrical frustration, which arises from the topology of a well-ordered structure rather than from disorder, has recently become a topic of considerable interest1. In particular, geometrical frustration among spins in magnetic materials can lead to exotic low-temperature states2, including ‘spin ice’, in which the local moments mimic the frustration of hydrogen ion positions in frozen water3,4,5,6. Here we report an artificial geometrically frustrated magnet based on an array of lithographically fabricated single-domain ferromagnetic islands. The islands are arranged such that the dipole interactions create a two-dimensional analogue to spin ice. Images of the magnetic moments of individual elements in this correlated system allow us to study the local accommodation of frustration. We see both ice-like short-range correlations and an absence of long-range correlations, behaviour which is strikingly similar to the low-temperature state of spin ice. These results demonstrate that artificial frustrated magnets can provide an uncharted arena in which the physics of frustration can be directly visualized.

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Figure 1: Illustration of frustration on the square lattice used in these experiments.
Figure 2: AFM and MFM images of a frustrated lattice.
Figure 3: Statistics of moment configurations.

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Acknowledgements

We acknowledge financial support from the Army Research Office and the National Science Foundation MRSEC programme, and discussions with P. Crowell and P. Lammert. R.S.F. thanks the CNPq-Brazil for sponsorship.

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Correspondence to P. Schiffer.

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Wang, R., Nisoli, C., Freitas, R. et al. Artificial ‘spin ice’ in a geometrically frustrated lattice of nanoscale ferromagnetic islands. Nature 439, 303–306 (2006). https://doi.org/10.1038/nature04447

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