Coupling of microwave magnetic dynamics in thin ferromagnetic films to stripline transducers in the geometry of the broadband stripline ferromagnetic resonance

TL;DR

This paper presents a quasi-analytical model for broadband ferromagnetic resonance in ferromagnetic films coupled to stripline transducers, highlighting how radiation losses depend on film conductivity, thickness, and measurement setup.

Contribution

The authors develop a simple analytical model for magnetization dynamics in ferromagnetic films coupled to striplines, enabling efficient simulations and analysis of radiation losses in FMR measurements.

Findings

Radiation losses are smaller in metallic films with high conductivity.

Increasing stripline width and using spacers reduce radiation losses.

Thicker films exhibit larger radiation losses.

Abstract

We constructed a quasi-analytical self-consistent model of the stripline-based broadband ferromagnetic resonance (FMR) measurements of ferromagnetic films. Exchange-free description of magnetization dynamics in the films allowed us to obtain simple analytical expressions. They enable quick and efficient numerical simulations of the dynamics. With this model we studied the contribution of radiation losses to the ferromagnetic resonance linewidth, as measured with the stripline FMR. We found that for films with large conductivity of metals the radiation losses are significantly smaller than for magneto-insulating films. Excitation of microwave eddy currents in these materials contributes to the total microwave impedance of the system. This leads to impedance mismatch with the film environment resulting in decoupling of the film from the environment and, ultimately, to smaller radiation losses. We also show that the radiation losses drop with an increase in the stripline width and when the sample is lifted up from the stripline surface. Hence, in order to eliminate this measurement artifact one needs to use wide striplines and introduce a spacer between the film and the sample surface. The radiation losses contribution is larger for thicker films.