Abstract:We report FePd 3 as a material for studying thermally active artificial spin ice (ASI) systems and use it to investigate both the square and kagome ice geometries. We readily achieve perfect ground state ordering in the square lattice and demonstrate the highest yet degree of monopole charge-ordering in the kagome lattice. We find that smaller lattice constants in the kagome system generally produce larger domains of charge order. Monte Carlo simulations show excellent agreement with our data when a small amount of disorder is included in the simulation.
Main text:Frustrated systems have emerged as an important topic of condensed matter physics, and geometric frustration is of particular prominence, where the frustration arises from an ordered structure rather than crystalline imperfections [1]. In such systems, an apparent degeneracy of ground states prevents long range order, often when detailed analysis of perturbations predict that an ordered state nevertheless should occur [2]. Despite decades of intense interest, frustrated systems still pose fundamental problems, with many unanswered questions, due in part to the tendency of these systems to inefficiently explore their configuration spaces and to lose ergodicity [3]. Monte Carlo simulations can address some of these issues, through the introduction of more complicated basic excitations [4,5], but questions about the specific
Frustrated systems, typically characterized by competing interactions that cannot all be simultaneously satisfied, display rich behaviours not found elsewhere in nature. Artificial spin ice takes a materials-by-design approach to studying frustration, where lithographically patterned bar magnets mimic the frustrated interactions in real materials but are also amenable to direct characterization. Here, we introduce controlled topological defects into square artificial spin ice lattices in the form of lattice edge dislocations and directly observe the resulting spin configurations. We find the presence of a topological defect produces extended frustration within the system caused by a domain wall with indeterminate configuration. Away from the dislocation, the magnets are locally unfrustrated, but frustration of the lattice persists due to its topology. Our results demonstrate the non-trivial nature of topological defects in a new context, with implications for many real systems in which a typical density of dislocations could fully frustrate a canonically unfrustrated system.
Using simple and inexpensive processing methodologies afforded by two‐stage reactive polymer networks (TSRPs) tunable mechanical anisotropy is displayed, defect‐independent guiding of cohesive fracture paths through soft material is demonstrated for the first time, and bio‐inspired microstructures are shown to enable performance enhancement beyond what is anticipated by the rule‐of‐mixtures in composites. The ability to pattern rubbery (stage I) and glassy (stage II) domains within a TSRP using photomasks and UV light is investigated through atomic force microscope (AFM) nanomechanical mapping techniques. AFM modulus mapping shows that the resulting stiffness anisotropy between stage I and stage II regions is length scale dependent. A gradient interface in elastic modulus between stage I and stage II materials is observed and, when patterned with an angled stage I pathway, the gradient interface exhibits remarkable resilience during failure, repeatedly deflecting cracks away from stage II regions, even while turning cracks at angles up to 135° When stage I and stage II domains are patterned in a nacre‐inspired microstructure, toughening beyond rule‐of‐mixtures’ prediction is observed.
Controlling the microstructure of heterogeneous, polymer membranes used in gas barrier and gas separation technologies is challenging. Being able to control composite structures is beneficial to achieve an optimum combination of gas permeation and mechanical performance. In addition, unique properties such as anisotropy and confined transport can be controlled by tailoring the size and position of constituent materials. Two-stage reactive polymer (TSRP) networks are an emerging dualcure polymer material for spatially varying cross-linking density via photopatterning. In this work a thiol−acrylate-based TSRP was used to investigate the effects of pattern geometry on CO 2 permeability and mechanical properties. Line and square patterns of alternating high and low cross-linking density, with characteristic dimension between 1 mm and 10 μm, were generated in TSRP membranes. Notably, synergistic enhanced barrier properties were observed for 10 μm square patterns of lower cross-linking density (or higher permeability) material exhibiting two confined dimensions compared to line gratings with only one confined dimension.
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