Engineering spin wave spectra in thick Ni$_{80}$Fe$_{20}$ rings by using competition between exchange and dipolar fields

TL;DR

This study investigates how the interplay between exchange and dipolar fields influences spin wave spectra in thick Ni80Fe20 rings, revealing non-monotonic mode intensity behavior through combined experimental and theoretical analysis.

Contribution

It introduces a theoretical model considering radial and axial mode profiles to explain non-monotonic spin wave spectra in thick ferromagnetic rings, supported by experimental validation.

Findings

Non-monotonic dependence of mode intensity on resonance field observed

Theoretical model matches experimental results well

Competition between exchange and dipolar fields causes unusual spectra behavior

Abstract

Control of the spin wave dynamics in nanomagnetic elements is very important for the realization of a broad range of novel magnonic devices. Here we study experimentally the spin wave resonance in thick ferromagnetic rings (100 nm) using perpendicular ferromagnetic resonance spectroscopy. Different from what was observed for the continuous film of the same thickness, or from ring with similar lateral dimensions but with lower thicknesses, the spectra of thick patterned rings show a non-monotonic dependence of the mode intensity on the resonance field for a fixed frequency. To explain this effect, the theoretical approach by considering the dependence of the mode profiles on both the radial and axial coordinates was developed. It was demonstrated that such unusual behavior is a result of the competition between exchange and dipolar fields acting at the spin excitations in the structure under study. The calculations are in a good agreement with the experimental results.