Microwave eddy-current shielding effect in metallic films and periodic nanostructures of sub-skin-depth thicknesses and its impact on stripline ferromagnetic resonance spectroscopy

Abstract

A strong microwave shielding effect due to the excitation of microwave eddy-currents exists for metallic films of sub-skin-depth thickness (10–100 nm). If the film is ferromagnetic, this effect strongly influences results of the broadband stripline ferromagnetic resonance (FMR) spectroscopy. It also potentially hampers the development of magnetically tuneable metamaterials. By means of rigorous numerical simulations, we address an important problem of the dependence of the eddy current effect on the width of the stripline used for driving magnetisation dynamics in the broadband FMR spectroscopy. We study theoretically electrodynamics of realistic striplines and also extend the main result from the case of continuous conductive films to periodic conductive nanostructures—magnonic crystals. Based on these findings, we also give recommendations on improving performance of magnetically tuneable metamaterials, which are based on conductive ferromagnetic films and nanostructures. In our simulations, we consider examples of microstrip lines which are 5 μm to 1.5 mm wide. However, the simulation results should be equally applicable to coplanar waveguides with the same width of the signal line.