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.

Methods
The experimental data in this work was collected via magnetic force microscopy (MFM), which provides black and white images indicating the magnetization of individual nanoislands in the measured arrays. The direction of each island can be categorized as +1 or -1 via image recognition and then analyzed by the included codes to recreate the work of the main manuscript. 

The simulation data in this work was produced via the software Mumax3. The scripts to run this were produced by included MatLab files.