Signature of magnetic monopole and Dirac string dynamics in spin ice
Abstract
Magnetic monopoles have eluded experimental detection since their prediction nearly a century ago by Dirac. It was recently shown that classical analogues of these enigmatic particles can occur as excitations out of the topological ground state of a model magnetic system, dipolar spin ice. These quasiparticle excitations do not require a modification of Maxwell's equations, but they do interact through Coulomb's law and are of magnetic origin. Here, we present an experimentally measurable signature of monopole dynamics. In particular, we show that previous magnetic relaxation measurements in the spinice material Dy_{2}Ti_{2}O_{7} (ref. 3) can be interpreted entirely in terms of the diffusive motion of monopoles in the grand canonical ensemble, constrained by a network of `Dirac strings' filling the quasiparticle vacuum. In a magnetic field, the topology of the network prevents charge flow in the steady state. Nevertheless, we demonstrate the existence of a monopole density gradient near the surface of an open system.
 Publication:

Nature Physics
 Pub Date:
 April 2009
 DOI:
 10.1038/nphys1227
 arXiv:
 arXiv:0903.1074
 Bibcode:
 2009NatPh...5..258J
 Keywords:

 Condensed Matter  Statistical Mechanics
 EPrint:
 Nature Phys.5:258261,2009