Tuning magnetic order with geometry: thermalisation and defects in two-dimensional artificial spin ices

Macauley, G. M. , Paterson, G. W. , Li, Y., Macêdo, R. , McVitie, S. and Stamps, R. L. (2020) Tuning magnetic order with geometry: thermalisation and defects in two-dimensional artificial spin ices. Physical Review B, 101, 144403. (doi: 10.1103/PhysRevB.101.144403)

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Abstract

Artificial spin ices are arrays of correlated nano-scale magnetic islands that prove an excellent playground in which to study the role of topology in critical phenomena. Here, we investigate a continuum of spin ice geometries, parameterised by rotation of the islands. In doing so, we morph from the classic square ice to the recently studied pinwheel geometry, with the rotation angle acting as a proxy for controlling inter-island interactions. We experimentally observe a transition from antiferromagnetic ordering in square ice to a slight preference for ferromagnetic vertices in the weakly-coupled pinwheel ice using Lorentz transmission electron microscopy on thermally annealed cobalt arrays. The rotation angle also affects the relaxation timescales for individual arrays, leading to varying degrees of thermalisation, and an apparent change in the nature of the defects supported: from one-dimensional strings in square ice to two-dimensional vortex-like structures for geometries similar to pinwheel. The numerical scaling of these quantities is consistent with that predicted by the Kibble-Zurek mechanism. Our results show how magnetic order in artificial spin ices can be tuned by changes in geometry and suggest the possibility of realising a truly frustrated ice-rule phase in two-dimensional systems. Furthermore, we demonstrate this system as a testbed to investigate out-of-equilibrium dynamics across phases.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Macauley, Mr Gavin and Paterson, Dr Gary and McVitie, Professor Stephen and Stamps, Professor Robert and Macedo, Dr Rair
Authors: Macauley, G. M., Paterson, G. W., Li, Y., Macêdo, R., McVitie, S., and Stamps, R. L.
College/School:College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
College of Science and Engineering > School of Physics and Astronomy
Journal Name:Physical Review B
Publisher:American Physical Society
ISSN:1098-0121
ISSN (Online):1550-235X
Copyright Holders:Copyright © 2020 American Physical Society
First Published:First published in Physical Review B 101:144403
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
168906Artificial spin ice: designer matter far from equilibriumStephen McVitieEngineering and Physical Sciences Research Council (EPSRC)EP/L002922/1P&S - Physics & Astronomy
190883Consortium for advanced materials based on spin chiralityStephen McVitieEngineering and Physical Sciences Research Council (EPSRC)EP/M024423/1P&S - Physics & Astronomy
172958A Focused Noble Gas Ion Beam Facility for Materials and Device Nanoanalysis - EQUIPMENT GRANTIan MacLarenEngineering and Physical Sciences Research Council (EPSRC)EP/P001483/1P&S - Physics & Astronomy