Abstract
In this paper we perform nanofabrication of square artificial spin ices with different lattice parameters, in order to investigate the roles of vertex excitation on the features of the system. In particular, the character of magnetic charge distribution asymmetry on the vertices are observed under magnetic hysteresis loop experiments. We then compare our results with simulation using an emergent Hamiltonian containing objects such as magnetic monopoles and dipoles in the vertices of the array (instead of the usual Hamiltonian based on the dipolar interactions among the magnetic nanoislands). All possible interactions between these objects are considered (monopole-monopole, monopole-dipole and dipole-dipole). Using realistic parameters we observe very good match between experiments and theory, which allow us to better understand the system dynamics in function of monopole charge intensity.
Highlights
Before describing the theoretical model we briefly summarize some well known facts about the square lattice investigated here
Electroresist was removed from the top of nanoisland by ashing in oxygen plasma
We have developed samples with three different lattice spacings of SQ0 = 3550 nm, SQ4 = 3950 nm and SQ8 = 4350 nm as an attempt to modify monopoles charge
Summary
Before describing the theoretical model we briefly summarize some well known facts about the square lattice investigated here. The ground state of the artificial square ice obeys the famous ice rule, which remains the familiar two-in, two-out (two spins must point in, while the other two must point out in each vertex). From this measurements, it is possible to observe all possible vertex configurations separated by classes having the same energy, indicated by T1, T2, T3 and T4 (see Fig. 1c). The first two categories (T1 and T2) obey the ice rule but the energy of these states is not degenerate (vertex configurations T1 has smaller energy than the ones with configurations T2). The ground-state of this system requires all vertices to be category T1
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