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Title: | Magnetisation processes in geometrically frustrated spin networks with self-assembled cliques |
Authors: | Tadic, B Andjelkovic, M Suvakov, M Rodgers, G |
Keywords: | spin dynamics;nanonetworks;simplex aggregation;hysteresis;antiferromagnetic defects |
Issue Date: | 14-Mar-2020 |
Publisher: | MDPI |
Citation: | Entropy, 2020, 22(3): 336 (15 pp.) |
Abstract: | (c) 2020 by the authors. Functional design of nanostructured materials seeks to exploit potential of complex morphologies and disorder. In this context, the spin dynamics in disordered antiferromagnetic materials present a significant challenge due to induced geometric frustration. Here we analyse the processes of magnetisation reversal driven by an external field in generalised spin networks with higher-order connectivity and antiferromagnetic defects. Using the model in [Tadic´ et al. Arxiv:1912.4331v1], we grow nanonetworks with geometrical constraint self-assembly of simplexes (cliques) of a given size n; with probability p each simplex possesses a defect edge affecting its binding, leading to a tree-like pattern of defects. The Ising spins are attached to vertices and have ferromagnetic interactions, while antiferromagnetic couplings apply between pairs of spins along each defect edge. Thus, a defect edge induces n −2 frustrated triangles per n-clique participating in a larger-scale complex. We determine several topological, entropy, and graph-theoretic measures to characterise the structure of these assemblies. Further, we show how the size of simplexes building the aggregates with a given pattern of defects affects the magnetisation curves, the length of the domain walls, and the shape of the hysteresis loop. The hysteresis shows a sequence of plateaus of fractional magnetisation and multi-scale fluctuations in the passage between them. For fully antiferromagnetic interactions, the loop splits into two parts only in mono-disperse assemblies of cliques consisting of an odd number of vertices n. At the same time, remanent magnetisation occurs when n is even, as well as in poly-disperse assemblies of cliques in the range n 2 [2, 10]. These results shed light on spin dynamics in complex nano-magnetic assemblies in which geometric frustration arises in the interplay of higher-order connectivity and antiferromagnetic interactions. |
URI: | https://bura.brunel.ac.uk/handle/2438/20495 |
DOI: | https://doi.org/10.3390/e22030336 |
ISSN: | 1099-4300 |
Appears in Collections: | Dept of Mathematics Research Papers |
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