Magnetic Study of Co-Doped Magnetosome Chains

Magnetotactic bacteria synthesize a chain of magnetic nanoparticles, called magnetosome chain, used to align and swim along the geomagnetic field lines. In particular, Magnetospirillum gryphiswaldense biomineralize magnetite, Fe3O4. Growing this species in a Co-supplemented medium, Co-doped magnetite is obtained, tailoring in this way the magnetic properties of the magnetosome chain. Combining structural and magnetic techniques such as transmission electron microscopy, energy-dispersive x-ray spectroscopy, X-ray absorption near edge structure, and X-ray magnetic circular dichroism, we determine that ∼1% of Co2+ substitutes Fe2+ located in octahedral places in the magnetite, thus increasing the coercive field. In the framework of the Stoner–Wohlfarth model, we have analyzed the evolution of the hysteresis loops as a function of temperature determining the different magnetic anisotropy contributions and their evolution with temperature. In contrast with the control magnetosome chains, whose effective anisot...