Effects of magnetic monopoles charge on the cracking reversal processes in artificial square ices

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.

Emergent Magnetic Monopole and Dipole Screening by Proximity Effect With Noble Metal

“…percentile of monopoles being generated in a sharp shape curve for lowest magnetic field. Those phenomena promoted by aluminum layer are qualitatively similar to what was observed in samples with different lattice parameters 37 where it was found that increasing distances among nanomagnets at the vertex reduces the stray field from the nanomagnets, affecting directly the magnetic monopole and dipole intensity. The present aluminum layer effect suggest fascinating interaction among metallic electron gas with emergent magnetic monopole and dipole, decreasing its intensity in a sort of electric screening.…”

“…To the best of our knowledge, experimental investigations or calculations of proximity effects by noble metals in nanostructures were not reported so far and in this work we are going to use an emergent excitation model 34 to investigate how the magnetization interface decrease in nanomagnets due to charge carrier excess would imply in the observed behavior of magnetization and monopole density in the reversal processes of an ASI. In our previous work 34,37 , numerical solution of a model of emergent excitations that considers the presence of magnetic monopoles of charge q and magnetic dipoles of moment | M| on the vertices, presented a qualitative match with the evolution of magnetization and monopole density in reversal process of experimental square ASI arrays 37 . In this model 34 , the total magnetic field at nanoisland i, B tot i , is the sum of the field produced by the excitations on the vertices (see Refs.…”

“…In this model 34 , the total magnetic field at nanoisland i, B tot i , is the sum of the field produced by the excitations on the vertices (see Refs. 34,37 for details). added to the external magnetic field.…”

“…In order to take into account differences among nanoislands, the h i values are drawn from a Gaussian distribution centered at h c with standard deviation σ d = σ h c . In our previous work 37 , we found that in order to qualitatively describe experimental results, a kind of bimodal distribution had to be used, in such a way that for 90% of the nanoislands, we used h c = h 90 c and σ 90 and for the remaining 10% of the islands different values, h c = h 10 c and σ 10 were used. In general, h x c will represent the mean switching field for x% of the nanoislands and σ x h x c the standard deviation of the gaussian distribution of switching fields for the same x% of the nanoislands.…”

“…The symbols represent the experimental data while solid curves are results from simulations averaged over 50 different distributions of switching fields. For the charge and dipole strengths we used the results we obtained in our previous work 37 , q = 0.5µ/a and M = 2.8µ. The reversal field distribution was manually adjusted to fit the experimental curves.…”