Fractional magnetic charges and channeling of Faraday lines by disclinations in artificial spin ice

We have studied the magnetic moments of artificial spin ice arrays of
nanomagnets in both undistorted square arrays and in arrays with
a topological defect induced by a single disclination. We confirm
that the disclination induces global, macroscopic changes in
the low-energy collective states of the nanomagnet moment
configuration. Specifically, the disclination leads to Faraday
lines of effective magnetic flux that run from the center all the
way to the edge of the arrays. Moreover, the geometric deformation,
induced by the topological defect, curves the geometry such that
these Faraday lines are channeled preferentially by the arrays’ curved
geometry. Our results demonstrate how the intentional combination
of topology and geometry can be designed to control magnetic charges
and the flow of local magnetization and thus manipulate
associated collective excitations.