Abstract
This letter describes the formation and detailed characterization of iron oxide mesocrystals produced by the directed assembly of superparamagnetic iron oxide-truncated nanocubes using the slow evaporation of the solvent within an externally applied homogeneous magnetic field. Anisotropic mesocrystals with an elongation along the direction of the magnetic field can be produced. The structure of the directed mesocrystals is compared to self-assembled mesocrystalline films, which are formed without the influence of a magnetic field. The remarkable structural difference of mesocrystals produced within the external magnetic field from those self-assembled without field indicates that the specific nanoparticle ordering within the superstructure is driven by competing of two types of anisotropic interactions caused by particle shape (i.e., faceting) and orientation of the magnetic moment (i.e., easy axes: <111>magnetite). Hence, these findings provide a fundamental understanding of formation mechanisms and structuring of mesocrystals built up from superparamagnetic nanoparticles and how a magnetic field can be used to design anisotropic mesocrystals with different structures.
Highlights
This can be useful to obtain increased magnetization while retaining the superparamagnetic properties of magnetite nanocrystals [16]
Nanoparticles and their assemblies belong to the hot research topics nowadays [1,2,3,4,5,6,7]
Assemblies consisting of superparamagnetic magnetite nanocrystals are still superparamagnetic their sizes can be tens or hundreds of micrometres [14,15]
Summary
This can be useful to obtain increased magnetization while retaining the superparamagnetic properties of magnetite nanocrystals [16]. Due to the superparamagnetic property of the magnetite nanocrystals, their assembly process can be strongly influenced by an external magnetic field which is labelled as “directed assembly” [21]. Superparamagnetic magnetite nanocrystals with an easy axis along magnetite give an extraordinary opportunity to investigate the assembly processes directed by an external magnetic field [22,23,24].
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