Difference between the Magnetic Properties of the Magnetotactic Bacteria and Those of the Extracted Magnetosomes: Influence of the Distance between the Chains of Magnetosomes

We report structural characterization and magnetic properties of various assemblies of chains of magnetosomes. The same magnetic properties are observed for the magnetotactic bacteria and for the extracted chains of magnetosomes isolated in a polymer. When the extracted chains of magnetosomes form a denser structure than that observed in the bacteria, the magnetic properties change markedly. A decrease in the coercivity and reduced remanence is observed. This behavior is attributed to an enhancement of the dipolar interactions between the chains of magnetosomes in the limit of a weakly interacting system; that is, the magnetostatic energy is lower than the anisotropy energy. The effect of the dipolar interactions is more pronounced at 250 K than at 10 K. This behavior is attributed to the existence of a family of small magnetosomes, which undergo a transition from a ferromagnetic to a superparamagnetic state.