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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 111,
B12S25,
15 PP., 2006
doi:10.1029/2006JB004529
Ferromagnetic resonance spectroscopy for assessment of magnetic anisotropy and magnetostatic interactions: A case study of mutant magnetotactic bacteria
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Osaka, Japan
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, USA
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
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.
Received 25 May 2006; accepted 25 October 2006; published 28 December 2006.
Citation: (2006), Ferromagnetic resonance spectroscopy for assessment of magnetic anisotropy and magnetostatic interactions: A case study of mutant magnetotactic bacteria, J. Geophys. Res., 111, B12S25, doi:10.1029/2006JB004529.
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