Artificial spin ice structures (ASI) have attracted great attention, serving as potential analogues for frustrated magnetic systems - such as bulk spin ice materials . In 2008, Castelnovo et al. realized that excitations above the degenerate ground state created by switching of a nanomagnet in a spinice vertex could be interpreted as emergent quasiparticles that behave like magnetic monopoles [2,3].
In this work, we discuss detailed investigations of magnetic switching behavior in individual vertices of square-ASI system composed of lithographically patterned nanoislands of dimensions 300×100×30 nm3 of Ni80Fe20. We demonstrate the possibility of controlled generation of an emergent magnetic monopole-like state in an isolated square ASI vertex. The interplay of defects and dipolar interactions appears to play a key role in determining the switchings of individual nanomagnets which can be used to create different emergent magnetic states at the ASI vertices.
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 C. Castelnovo, et al., Nature 451, 42 (2008).
 A. Farhan, et al., Science Advances 5, eaav6380 (2019).