Influence of the presence of multiple resonances on material parameter determination using broadband ferromagnetic resonance spectroscopy

The influence of the presence of multiple resonances in ferromagnetic resonance spectra on extracted material parameters is investigated using numerical simulations. Our results show that the systematic error of assuming an incorrect number of resonances for a material can lead to the extraction of material parameters that significantly deviate from any of the true material parameters. When noise is present in experimental ferromagnetic resonance spectra increasing the frequency range of the broadband characterization can significantly reduce the error-margins when the data is analyzed assuming the correct number of resonances present in the material. For the cases investigated in this study it was found that analyzing the data using a single resonance results in extracted gyromagnetic ratios and effective magnetization parameters that are consistent with the weighted average of the true material parameters. We further provide a cautionary example regarding the extraction of the inhomogeneous linewidth broadening and damping parameters of materials that contain an unknown number of resonances.