Neumann, S. / Kuger, L. / Arlt, C.-R. / Franzreb, M./ Rafaja, D. (2023)

Scientific Reports, 2023,13:5673

Abstract

Magnetic properties of superparamagnetic iron oxide nanoparticles are controlled mainly by their
particle size and by their particle size distribution. Magnetic properties of multi‑core iron oxide
nanoparticles, often called iron oxide nanoflowers (IONFs), are additionally affected by the interaction
of magnetic moments between neighboring cores. The knowledge about the hierarchical structure of
IONFs is therefore essential for understanding the magnetic properties of IONFs. In this contribution,
the architecture of multi‑core IONFs was investigated using correlative multiscale transmission
electron microscopy (TEM), X‑ray diffraction and dynamic light scattering. The multiscale TEM
measurements comprised low‑resolution and high‑resolution imaging as well as geometric phase
analysis. The IONFs contained maghemite with the average chemical composition γ‑Fe2.72±0.02O4 . The
metallic vacancies located on the octahedral lattice sites of the spinel ferrite structure were partially
ordered. Individual IONFs consisted of several cores showing frequently a specific crystallographic
orientation relationship between direct neighbors. This oriented attachment may facilitate
the magnetic alignment within the cores. Individual cores were composed of partially coherent
nanocrystals having almost the same crystallographic orientation. The sizes of individual constituents
revealed by the microstructure analysis were correlated with the magnetic particle sizes that were
obtained from fitting the measured magnetization curve by the Langevin function.

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