Ferromagnetic resonance characterization of greigite (Fe3S4), monoclinic pyrrhotite (Fe7S8), and non-interacting titanomagnetite (Fe3-xTixO4)

Ferromagnetic resonance (FMR) spectroscopy has become an increasingly useful tool for studying the magnetic properties of natural samples. Magnetite (Fe3O4) is the only magnetic mineral that has been well characterized using FMR. This limits the wider use of FMR in rock magnetism and paleomagnetism. In this study, we applied FMR analysis to a range of magnetic minerals, including greigite (Fe3S4), monoclinic pyrrhotite (Fe7S8), magnetically non-interacting titanomagnetite (Fe3-xTixO4), and synthetic magnetite chains to constrain interpretation of FMR analysis of natural samples and to explore applications of FMR spectroscopy. We measured the FMR signatures of a wide range of well-characterized samples at the X-and Q-bands. FMR spectra were also simulated numerically to compare with experimental results. The effects of magnetic anisotropy, mineralogy, domain state, and magnetostatic interactions on the FMR spectra are discussed for all studied minerals. Our experimental and theoretical analyses of magnetically non-interacting tuff samples and magnetically interacting chains enable quantitative assessment of contributions of magnetostatic interactions and magnetic anisotropy to the FMR spectra. Our results also indicate that intact magnetosomes are a unique system with distinct FMR signatures. While FMR analysis is useful for characterizing magnetic properties of natural samples, care is needed when making interpretations because of overlaps in a range of FMR signatures of different magnetic minerals with different magnetic properties. Our analyses will help to constrain such interpretations in rock magnetic studies.