Magnetic monopole free motion in two-dimensional artificial spin ice.

This article focuses on the experimental observation of free magnetic monopole motion in two-dimensional artificial spin ice (ASI) systems with rectangular lattice geometries. By fabricating rectangular ASI arrays with varying aspect ratios, particularly at the ratio \( a/b = \sqrt{3} \), the study demonstrates that magnetic monopoles can move freely under external magnetic fields due to ground-state degeneracy that reduces string tension connecting monopole pairs. Magnetic force microscopy measurements reveal monopole creation, transport, and annihilation, with monopoles leaving tensionless strings connected to charges at sample borders, contrasting with conventional square ASI where monopoles remain bound by energetic strings. These findings suggest that rectangular ASI provides a simpler planar platform for magnetricity applications at room temperature, enabling controlled magnetic charge currents without the complexities of three-dimensional ASI fabrication.