Collective magnetism in an artificial 2D XY spin system
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Two-dimensional magnetic systems with continuous spin degrees of freedom exhibit a rich spectrum of thermal behaviour due to the strong competition between fluctuations and correlations. When such systems incorporate coupling via the anisotropic dipolar interaction, a discrete symmetry emerges, which can be spontaneously broken leading to a low-temperature ordered phase. However, the experimental realisation of such two-dimensional spin systems in crystalline materials is difficult since the dipolar coupling is usually much weaker than the exchange interaction. Here we realise two-dimensional magnetostatically coupled XY spin systems with nanoscale thermally active magnetic discs placed on square lattices. Using low-energy muon-spin relaxation and soft X-ray scattering, we observe correlated dynamics at the critical temperature and the emergence of static long-range order at low temperatures, which is compatible with theoretical predictions for dipolar-coupled XY spin systems. Furthermore, by modifying the sample design, we demonstrate the possibility to tune the collective magnetic behaviour in thermally active artificial spin systems with continuous degrees of freedom.
Leo , N , Holenstein , S , Schildknecht , D , Sendetskyi , O , Luetkens , H , Derlet , P M , Scagnoli , V , Lançon , D , Mardegan , J R L , Prokscha , T , Suter , A , Salman , Z , Lee , S & Heyderman , L J 2018 , ' Collective magnetism in an artificial 2D XY spin system ' , Nature Communications , vol. 9 , no. 1 , 2850 . https://doi.org/10.1038/s41467-018-05216-2
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DescriptionThis work was funded by the Swiss National Science Foundation (SNSF project grants 200021-155917, 200021-159736, and 200021-172774). D.L. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No 701647. J.R.L.M. is grateful to the Swiss National Center of Competence in Research, Molecular Ultrafast Science and Technology (NCCR MUST).
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