  Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic
bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic
magnetite NC chain-like assemblies is reported. An easy green synthesis route
in a thermoreversible gelatin hydrogel matrix is used. The structure of these
magnetite chains prepared with and without gelatin is characterized by means of
transmission electron microscopy, including electron tomography (ET). These
structures indeed bear resemblance to the magnetite assemblies found in MTB,
known for their mechanical flexibility and outstanding magnetic properties and
known to crystallographically align their magnetite NCs along the strongest
<111> magnetization easy axis. Using electron holography (EH) and angular
dependent magnetic measurements, the magnetic interaction between the NCs and
the generation of a magnetically anisotropic material can be shown. The
electro- and magnetostatic modeling demonstrates that in order to precisely
determine the magnetization (by means of EH) inside chain-like NCs assemblies,
their exact shape, arrangement and stray-fields have to be considered (ideally
obtained using ET).
