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Ferromagnetic resonance and magnetic characteristics of intact magnetosome chains in magnetospirillum gryphiswaldense

Ferromagnetic resonance and magnetic characteristics of intact magnetosome chains in magnetospirillum gryphiswaldense
chair:

Fischer, H. / Mastrogiacomo, G. / Löffler, J.F. / Warthmann, R.J. / Weidler, P.G. / Gehring, A.U. (2008)

place:

Earth Planet Sci Let., 270 (2007), 3-4, 200-208

Date: 2008

Fischer, H. / Mastrogiacomo, G. / Löffler, J.F. / Warthmann, R.J. / Weidler, P.G. / Gehring, A.U. (2008): „Ferromagnetic resonance and magnetic characteristics of intact magnetosome chains in magnetospirillum gryphiswaldense“. In: Earth Planet Sci Let., 270 (2008), 3-4, 200-208

Abstract

The magnetic characteristics of intact magnetosome chains in Magnetospirillum gryphiswaldense bacteria were investigated by means of static and dynamic magnetic analyses and ferromagnetic resonance spectroscopy. The nano-sized magnetosomes are generally in a stable single-domain state, but magnetosomes smaller than 30 nm characteristic of superparamagnetic magnetite particles were also found. Alternating current (AC) susceptibility indicates that all magnetosomes are blocked below 150 K.

At room temperature the anisotropy of M. gryphiswaldense is dominated by the shape of the magnetosome chains. Low-temperature ferromagnetic resonance (FMR) spectroscopy indicates that this dominant shape anisotropy can affect the detection of the Verwey transition at 100 K. The static and dynamic magnetic analyses show that the Verwey transition is smeared and that our magnetotactic bacteria fail the Moskowitz test.

This failure is explained by the biomineralization of non-stoichiometric magnetosomes. This interpretation is based on the increase in high-field susceptibility and the distinct peak in the out-of-phase component of the AC susceptibility below 50 K. These results are attributed to freezing of spins associated with defect structures in the core and at the surface of nano-sized magnetosomes. The results obtained from M. gryphiswaldense demonstrate that intrinsic properties of nano-sized magnetosomes are significantly influenced by non-stoichiometry and by the anisotropy excited from their arrangement in the bacteria.


 

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