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Magnetism

Monopoles on the move

Nature Physics volume 5, pages 250–251 (2009)Cite this article

Magnetic materials provide a new context for observing magnetic monopoles. Numerical simulations now establish an experimentally measurable signature of their dynamics — one that has in fact already been seen in a spin-ice compound.

In contrast to their electrical counterparts, isolated magnetic charges are not readily observed in nature. Despite much experimental effort invested in their search, they always seem to come in pairs, with opposite polarity, leaving no net charge behind. Just like a compass needle, which has two poles, if we were to break magnetic dipoles apart, the resulting constituents would still retain their dipolar nature. However, in a recent paper1 it was argued that magnetic monopoles could form as objects that emerge from the collective behaviour of the atomic moments in a class of exotic materials collectively known as 'spin ice'2, rather than as free elementary particles. Now a numerical analysis by Ludovic Jaubert and Peter Holdsworth, reported on page 258 of this issue3, indicates that monopole dynamics accounts for previously unexplained experimental data4 in one of the canonical spin-ice materials, Dy2Ti2O7, providing persuasive evidence of the role of monopoles as the fundamental and dominant excitations in such systems. The presence of monopole excitations in spin ice signals a new, three-dimensional, manifestation of the phenomenon of fractionalization — the constituent degrees of freedom (in this case, the magnetic dipoles associated with the rare-earth ions) combine to yield excitations that look like fragments of dipoles.

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Figure 1: Magnetic monopole creation and dynamics in spin ice.

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Authors and Affiliations

  1. Max-Planck-Institut für Physik komplexer Systeme, Dresden, 01187, Germany

    Roderich Moessner

  2. Department of Physics and Materials Research Institute, Pennsylvania State University, 104 Davey Laboratory, University Park, 16802, Pennsylvania, USA

    Peter Schiffer

Authors
  1. Roderich Moessner
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  2. Peter Schiffer
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Moessner, R., Schiffer, P. Monopoles on the move. Nature Phys 5, 250–251 (2009). https://doi.org/10.1038/nphys1244

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