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Published December 28, 2006 | Supplemental Material + Updated
Journal Article Open

Ferromagnetic resonance spectroscopy for assessment of magnetic anisotropy and magnetostatic interactions: A case study of mutant magnetotactic bacteria


Ferromagnetic resonance spectroscopy (FMR) can be used to measure the effective magnetic field within a sample, including the contributions of both magnetic anisotropy and magnetostatic interactions. One particular use is in the detection of magnetite produced by magnetotactic bacteria. These bacteria produce single-domain particles with narrow size and shape distributions that are often elongated and generally arranged in chains. All of these features are detectable through FMR. Here, we examine their effects on the FMR spectra of magnetotactic bacteria strains MV-1 (which produces chains of elongate magnetite crystals), AMB-1 (which produces chains of nearly equidimensional magnetite crystals), and two novel mutants of AMB-1: mnm13 (which produces isolated, elongate crystals), and mnm18 (which produces nearly equidimensional crystals that are usually isolated). Comparison of their FMR spectra indicates that the positive magnetic anisotropy indicated by the spectra of almost all magnetotactic bacteria is a product of chain alignment and particle elongation. We also find correlations between FMR properties and magnetic measurements of coercivity and magnetostatic interactions. FMR thus provides a rapid method for assessing the magnetic properties of assemblages of particles, with applications including screening for samples likely to contain bacterial magnetofossils.

Additional Information

Author postprint. Published version -- © 2006 American Geophysical Union. Received 25 May 2006; revised 28 September 2006; accepted 25 October 2006; published 28 December 2006. We thank Angelo Di Bilio for assistance with the EPR spectrometer, Arash Komeili for assistance with the mutagenesis, and Mike Jackson, David Griscom, and an anonymous reviewer for helpful comments. The Beckman Institute provided support for the use of the MPMS. R.E.K., J.L.K., and C.Z.N. would like to thank the Agouron Institute, the Moore Foundation, and the NASA Astrobiology Science and Technology Instrument Development program for support. A.K. was partially supported by funds from a New Energy and Industrial Technology Development Organization fellowship. D.A.B. was supported by U.S. National Science Foundation grant EAR-0311950. B.P.W. thanks the NASA Mars Fundamental Research and NSF Geophysics Programs. This special section is based on the session "Rock Magnetism: Fundamentals and Frontiers" held at the 2005 AGU Fall Meeting. JGR 111, B12S25

Attached Files

Supplemental Material - 2006JB004529-matFMR-1.0.zip

Supplemental Material - KOPjgrb06readme.txt

Updated - Kopp2006-FMR-mutants.pdf


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