Microwave magnetoelectric fields: An analytical study of topological characteristics

TL;DR

This paper analytically investigates the topological properties of magnetoelectric fields generated by ferrite disks with magnetic-dipolar-mode oscillations, revealing fundamental features and potential coupling effects not observable numerically.

Contribution

It introduces an analytical method to characterize the topological structure of ME fields, including edge effects, distinguishing eigen topological features from external radiation.

Findings

Analytical topological structure of ME fields outside ferrite disks.

Identification of phenomena related to Tellegen and bianisotropic effects.

Distinction between eigen ME fields and external electromagnetic radiation.

Abstract

The near fields originated from a small quasi-two-dimensional ferrite disk with magnetic-dipolar-mode (MDM) oscillations are the fields with broken dual (electric-magnetic) symmetry. Numerical studies show that such fields, called the magnetoelectric (ME) fields, are distinguished by the power-flow vortices and helicity parameters [E. O. Kamenetskii, R. Joffe, and R. Shavit, Phys. Rev. E 87, 023201 (2013)]. These numerical studies can well explain recent experimental results with MDM ferrite disks. In the present paper, we obtain analytically topological characteristics of the ME-field modes. For this purpose, we use a method of successive approximations. In the second approximation we take into account the influence of the edge regions of an open ferrite disk, which are excluded in the first-approximation solving of the magnetostatic (MS) spectral problem. Based on the analytical method, we obtain a 'pure' structure of the electric and magnetic fields outside the MDM ferrite disk. The analytical studies can display some fundamental features that are non-observable in the numerical results. While in numerical investigations, one cannot separate the ME fields from the external electromagnetic (EM) radiation, the present theoretical analysis allows clearly distinguish the eigen topological structure of the ME fields. Importantly, this ME-field structure gives evidence for certain phenomena that can be related to the Tellegen and bianisotropic coupling effects. We discuss the question whether the MDM ferrite disk can exhibit properties of the cross magnetoelectric polarizabilities.