Regensburg 2019 – wissenschaftliches Programm
MA 27.3: Hauptvortrag
Mittwoch, 3. April 2019, 11:15–11:35, H38
The influence of defects in individual biogenic magnetite nanocrystals on their magnetic properties — •R. E. Dunin-Borkowski1, A. Kovács1, and M. Pósfai2 — 1Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, Jülich, Germany — 2Department of Earth and Environmental Sciences, University of Pannonia, Veszprém, Hungary
The cells of magnetotactic bacteria can be regarded as model systems for studying the magnetic properties of ferrimagnetic nanocrystals. Each bacterial strain produces magnetosomes that have distinct sizes, shapes, crystallographic orientations and spatial arrangements. By studying the magnetic behaviour of magnetosomes in appropriately chosen strains, the competing effects that influence the magnetic moments and microstructures of individual particles and their assemblages can be assessed and understood separately. The effect of particle size on magnetic domain character, the influence of shape and magnetocrystalline anisotropy on the direction of the magnetic induction within and between particles, the changes that are imposed on the magnetic behaviour of particles by their interactions and the effects of structural imperfections on magnetic moments can all be studied.
We have used off-axis electron holography, an advanced transmission electron microscopy (TEM) technique, to study the magnetic properties of individual and closely-spaced magnetite magnetosomes, alongside conventional TEM measurements of the structures, orientations and morphologies of the magnetosomes. We studied magnetite magnetosomes with elongated bullet-like shapes and different crystallographic axes of elongation, as well as magnetosomes that were either twinned or composed of several crystals. In this way, the effect of crystallography and structural imperfections on the magnetic properties of individual magnetite nanocrystals could be studied .
 We are grateful to D. Faivre, D. Schüler, C. T. Lefèvre, R. Uebe, D. A. Bazylinski, R. B. Frankel, E. Tompa and for valuable contributions to this work.