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Thermally and field-driven mobility of emergent magnetic charges in square artificial spin ice.

  • Author(s): Morley, Sophie A
  • Porro, Jose Maria
  • Hrabec, Aleš
  • Rosamond, Mark C
  • Venero, Diego Alba
  • Linfield, Edmund H
  • Burnell, Gavin
  • Im, Mi-Young
  • Fischer, Peter
  • Langridge, Sean
  • Marrows, Christopher H
  • et al.
Abstract

Designing and constructing model systems that embody the statistical mechanics of frustration is now possible using nanotechnology. We have arranged nanomagnets on a two-dimensional square lattice to form an artificial spin ice, and studied its fractional excitations, emergent magnetic monopoles, and how they respond to a driving field using X-ray magnetic microscopy. We observe a regime in which the monopole drift velocity is linear in field above a critical field for the onset of motion. The temperature dependence of the critical field can be described by introducing an interaction term into the Bean-Livingston model of field-assisted barrier hopping. By analogy with electrical charge drift motion, we define and measure a monopole mobility that is larger both for higher temperatures and stronger interactions between nanomagnets. The mobility in this linear regime is described by a creep model of zero-dimensional charges moving within a network of quasi-one-dimensional objects.

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