Physicists have searched for decades for magnets with a single pole. Now, two independent groups report the latest signatures of magnetic monopoles in a class of crystalline materials called spin ice. When the crystals were chilled to near absolute zero, they seemed to fill with tiny single points of north and south separated by fractions of a nanometre. Jonathan Morris at the Helmholtz Centre for Materials and Energy in Berlin and his colleagues used Dy2Ti2O7, whereas Tom Fennell at the Institute Laue–Langevin in Grenoble, France, and his collaborators used Ho2Ti2O7.
The atoms in the crystals sit at the corners of tetrahedra. Each atom behaves like a tiny bar magnet, and when the crystal is cooled, the atoms align to create regions of north or south magnetic charge, separated by a chain of aligned atoms (see image). The charge isn't attached to any physical object, but it behaves like a monopole.
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For a longer story on this research, see http://tinyurl.com/monopole
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Physics: Magnetic monopoles. Nature 461, 148 (2009). https://doi.org/10.1038/461148c
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DOI: https://doi.org/10.1038/461148c
