Letter

Nature 439, 303-306 (19 January 2006) | doi:10.1038/nature04447; Received 16 August 2005; Accepted 16 November 2005

There is an Addendum (1 March 2007) associated with this document.

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

R. F. Wang1, C. Nisoli1, R. S. Freitas1, J. Li1, W. McConville1, B. J. Cooley1, M. S. Lund2, N. Samarth1, C. Leighton2, V. H. Crespi1 & P. Schiffer1

  1. Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
  2. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA

Correspondence to: P. Schiffer1 Correspondence and requests for materials should be addressed to P.S. (Email: schiffer@phys.psu.edu).

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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