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Observation of a Coulomb phase in a 2D array of frustrated magnets - Yann Perrin

Frustration appears in a physical system when it is impossible to minimise simultaneously all the pairwise interactions. Frustration exists in some particular rare-earth compounds, such as Ho2Ti2O7 [1]. Because of some common characteristics they share with water ice, physicists call these compounds "spin ices". Their internal frustration gives rise to unusual magnetic properties, like a residual entropy, or monopole-like excitations [2]. However, experimental techniques are unable to probe each spin individually within these compounds.

In 2006 Wang et al. opened a new way for studying magnetically frustrated spin systems [3]. Using e-beam lithography, one can make arrays of magnetic islands with the desired design. The state of each nanomagnet can be probed individually in real space at room temperature using magnetic imaging (e.g. Magnetic Force Microscopy). It allows to study locally how the system accommodates to frustration. During this seminar, I will present a short overview of these "artificial spin ices", focused on the square geometry. Then, I will present our recent experimental study of a two-dimensional Coulomb phase in artificial square ice [4].

[1] M.J. Harris et al., Phys. Rev. Lett. 79, 2554 (1997).
[2] C. Castelnovo et al., Nature 451, 7174 (2008).
[3] R.F. Wang et al., Nature 439, 303 (2006).
[4] Y. Perrin et al., Nature 540, 410 (2016).