Abstract
Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.
Highlights
Ice I phase is characterised by the individual bars being treated as dipolar needles approximated by a dumbbell
Each dumbbell can be be in one of two antiparallel states but no vertex can be in a state representing an ice rule violation
The path chosen at the out-vertex is controlled by the domain wall chirality i.e. topology, independent of whether the system supports transverse domain walls[5] or vortex domain walls[28]
Summary
They observe time dependent switching above 30 K which they attribute either to the existence of multiple energy barriers or to the existence of numerous metastable states during the overcoming of a single energy barrier Perhaps these two pictures are in some sense the same.it is important to note that in uncapped permalloy wires exchange bias effects due to the oxide layer becoming antiferromagnetic below 20 K can potentially influence the pinning and depinning of ferromagnetic domain walls[30].
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