Imaging the stray field of chiral artificial spin ice with scanning nanoSQUID-on-tip

We use a scanning nanometer-scale superconducting quantum interference device (nanoSQUID) [1] to image the stray field of an artificial spin ice, which displays structural chirality. Experiments are carried out in a series of magnetic fields at 4.2 K. The "chiral ice" [2] is a 2D arrangement of lithographically patterned permalloy nanomagnets. Each stadium-shaped nanomagnet is much thinner than its in-plane dimensions, producing a strong shape anisotropy that favors a single-domain magnetization configuration [3]. Neverthelesss, scanning nanoSQUID measurements, backed by micromagnetic simulations, show that the magnetization in the nanomagnets is not uniform, displaying a bending at the edges of the nanostructures. The results show that the number of degrees of freedom in artificial spin ice can be much larger than typically captured in dipolar models. These additional degrees of freedom contribute to the field-induced dynamics and may be used to create reprogrammable magnonic crystals [4].

[1] D. Vasyukov et al., Nat. Nanotech. 8, 639 (2013); D. Vasyukov et al., Nano Lett. 18. 964 (2018).
[2] S. Gliga, et al., Nat. Mater. 16, 1106 (2017).
[3] A. Farhan et al., Phys. Rev. Lett. 111, 057204 (2013).
[4] E. Iacocca and O. Heinonen, Phys. Rev. Appl. 8, 034015 (2017).