Ferromagnetic resonance of magnetite biominerals traces redox changes

Magnetic Properties of Bacterial Magnetosomes Produced by Magnetospirillum caucaseum SO-1

“…The spectrum is an asymmetric inhomogeneously broadened line (∆ B pp ~167 mT), with the shape characteristic for EPR spectra of Fe 3+ cations coupled by a strong exchange interaction between ions in different charge states [ 66 ]. This shape of the resonance curve is commonly observed in magnetite from fossilized MTB [ 21 , 67 , 68 ], where the grains have a lognormal size distribution and are arranged mainly in chaotic aggregates rather than in ordered chains [ 69 ], in agreement with electron microscopy observations. The spectrum can be decomposed into two symmetric Gaussian components with g -factors of 2.01 and 2.32, respectively.…”

“…Magnetic properties of biogenic magnetite from magnetofossils are studied using standard paleo- and rock magnetism methods such as alternating fields or, in some cases, thermal demagnetization, and measurement of hysteresis loops, isothermal remanent magnetization acquisition curves, and saturation isothermal remanent magnetization (SIRM) demagnetization by dc magnetic field of the opposite sign (backfield curves). More advanced approaches include construction of first-order reversal curve diagrams [ 18 , 19 ], SIRM measurements at cryogenic temperatures [ 20 ], and ferromagnetic resonance (FMR) spectroscopy [ 21 ]. The influence of the external environment leads to a change in the chemical composition and structure of biogenic magnetite: Stable under slightly alkaline conditions of sea bottom sediments [ 22 ], it is partially or completely converted to maghemite during oxidation in freshwater conditions [ 6 ].…”

Non‐Chained, Non‐Interacting, Stable Single‐Domain Magnetite Octahedra in Deep‐Sea Red Clay: A New Type of Magnetofossil?

“…Ferromagnetic resonance (FMR) is sensitive to the magnetic anisotropy of SSD particles, and it has been used to detect and classify magnetofossils (e.g., Blattmann et al., 2020; Kopp et al., 2006; Kumagai et al., 2018; Usui et al., 2019; Weiss et al., 2004a). We measured FMR on one Unit II sample (36.5 m).…”

Magnetotactic Bacteria and Magnetosomes: Basic Properties and Applications

“…Methods used for the analysis included thermal and alternating field demagnetization of natural remanent magnetization, measurement of hysteresis loops, and curves of isothermal saturation remanent magnetization and anhysteretic remanent magnetization. More advanced methods such as construction of first order reversal curve (FORC) diagrams [77,158] and ferromagnetic resonance spectroscopy (FMR) [159] have been applied to selected samples.…”