Abstract
We demonstrate the use of an external field to stabilize and control defect lines connecting topological monopoles in spin ice. For definiteness we perform Brownian dynamics simulations with realistic units mimicking experimentally realized artificial colloidal spin ice systems, and show how defect lines can grow, shrink or move under the action of direct and alternating fields. Asymmetric alternating biasing forces can cause the defect line to ratchet in either direction, making it possible to precisely position the line at a desired location. Such manipulation could be employed to achieve mobile information storage in these metamaterials.
Highlights
IntroductionSystems mimicking the behavior of spin ice have been studied experimentally and theoretically for nanomagnetic islands[1,2,3,4,5,6,7,8,9,10,11], superconducting vortices[12,13,14], and paramagnetic colloidal particles on photolithographically etched surfaces[13, 15,16,17]
Four paramagnetic colloidal particles are each trapped in the gravitational wells by the combination of their own apparent weight (W = (ρ − ρliquid)gV) and the normal force from the wall, where ρ is the density and V is the volume of an individual particle, ρliquid is the density of the surrounding liquid, and g is the gravitational constant
We have shown that a defect line in a colloidal spin ice system contracts spontaneously at a rate which increases as the colloid-colloid interaction strength is increased
Summary
Systems mimicking the behavior of spin ice have been studied experimentally and theoretically for nanomagnetic islands[1,2,3,4,5,6,7,8,9,10,11], superconducting vortices[12,13,14], and paramagnetic colloidal particles on photolithographically etched surfaces[13, 15,16,17] In each of these particle-based artificial ice systems, the collective lowest energy state is embedded into an ice-manifold where all vertices obey the “2-in/2-out” ice rule: two particles are close to each vertex and two are far from it. It is possible to write information into such a manifold by using an MFM tip[11] or an optical tweezer[15] to generate topological defects in the ground state arrangement of the spins These defects consist of vertices that violate the ice rule and correspond to 3-in/1-out or 3-out/1-in configurations. By moving localized packets of information with a global force, it is possible to parallelize the information storage and retrieval procedures, increasing the speed in both cases
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