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Originally published in Science Express on 3 September 2009
Science 16 October 2009:
Vol. 326. no. 5951, pp. 411 - 414
DOI: 10.1126/science.1178868
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Reports

Dirac Strings and Magnetic Monopoles in the Spin Ice Dy2Ti2O7

D. J. P. Morris,1,* D. A. Tennant,1,2,* S. A. Grigera,3,4,* B. Klemke,1,2 C. Castelnovo,5 R. Moessner,6 C. Czternasty,1 M. Meissner,1 K. C. Rule,1 J.-U. Hoffmann,1 K. Kiefer,1 S. Gerischer,1 D. Slobinsky,3 R. S. Perry7

Sources of magnetic fields—magnetic monopoles—have so far proven elusive as elementary particles. Condensed-matter physicists have recently proposed several scenarios of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin-ice state is argued to be well described by networks of aligned dipoles resembling solenoidal tubes—classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defects look like magnetic monopoles. We demonstrated, by diffuse neutron scattering, the presence of such strings in the spin ice dysprosium titanate (Dy2Ti2O7). This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate the density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.

1 Helmholtz-Zentrum Berlin für Materialien und Energie, Glienicker Str. 100, D-14109 Berlin, Germany.
2 Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany.
3 School of Physics and Astronomy, North Haugh, St. Andrews, Fife KY15 9SS, UK.
4 Instituto de Física de Líquidos y Sistemas Biológicos, CONICET, UNLP, La Plata, Argentina.
5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK.
6 Max-Planck-Institut für Physik Komplexer Systeme, Nöthnitzer Str. 38, D-01187 Dresden, Germany.
7 School of Physics, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK.

* To whom correspondence should be addressed. E-mail: jonathan.morris{at}helmholtz-berlin.de (D.J.P.M.); tennant{at}helmholtz-berlin.de (D.A.T); sag{at}iflysib.unlp.edu.ar (S.A.G.)

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Observing Monopoles in a Magnetic Analog of Ice.
M. J. P. Gingras (2009)
Science 326, 375-376
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