Excitation of spin waves in the presence of magnetic charges and monopole polarons in finite-size square artificial spin ice systems

Abstract

Artificial spin ice (ASI) is a special class of engineered lattice of highly shape anisotropic single domain magnetic nanostructures, which is used as one of the model systems to study the spin ice behavior observed in pyrochlore oxides. The nanomagnets interact via dipolar interaction, resulting in correlated magnetization dynamics exhibiting macroscopic spin configuration states. Here, we exploit the tunability of magnetic microstates in the presence of an external field to study the excitation of spin waves in a finite-size square artificial spin ice system due to a locally applied pulse field. Also, we have studied the excitation in other nanomagnets which are not subjected to the pulse field, which we term as ``propagation'' of the waves from the perturbed nanomagnets to unperturbed ones purely due to the dipolar coupling. We report that careful selection of vertices with local magnetic charges can effectively direct the anisotropic spin wave excitation in neighboring nanomagnets in the presence of an external field. Further, the investigation has been carried out for spin wave excitation due to the magnetic monopole-polaronic environment forming in closed-edge ASI vertices. Our studies based on micromagnetic simulations suggest that magnetically charged vertices and monopole-polaron formation in square ASI vertices carry spectral signatures such as splitting in higher-frequency bulk mode.