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@INPROCEEDINGS{Sun:906825,
author = {Sun, Xiao and Tayal, A. and Dippel, A.-C. and Petracic, O.},
title = {{T}uning the structural and magnetic properties of iron
oxide nanoparticles},
reportid = {FZJ-2022-01719},
year = {2022},
abstract = {Due to their biocompatibility and magnetic properties, iron
oxide nanoparticles (NPs) areespecially interesting for
applications such as targeted drug delivery and hyperthermia
therapy[1–3]. According to its oxidation states, iron may
form various crystal structures and thus showdifferent
magnetic properties. Divalent FeO is a bulk antiferromagnet
with a rock salt crystalstructure at room temperature. When
Fe2+ is oxidized towards the trivalent state, as found e.g.
inFe3O4 and Fe2O3, one encounters a spinel structure and
ferrimagnetic (FiM) behavior. The FiM toparamagnetic phase
transition for bulk magnetite and maghemite occurs at TC =
858K and 948K,respectively. However, they may show different
magnetic properties in nanoscale due to thefinite size
effect. Synthesis of single-phase oxide NPs is challenging.
An oxidized layer is oftenfound at the surface of the NPs.
This leads to an exchange bias effect.We observe a shift in
the hysteresis loops of various sizes of iron oxide NPs
(5-20nm). This isdue to an exchange interaction between the
magnetite core and a shell with disordered surfacespins. By
comparing hysteresis loops cooled at different magnetic
fields, a hardening effect isobserved, i.e. the squareness
and hardness of hysteresis loops is significantly enhanced
withincreasing magnetic cooling field. This indicates that
an anisotropy axis is induced due to theexchange bias
effect.In order to understand the origin of the exchange
bias effect, we studied their crystallographicstructure
using X-ray powder diffraction, total scattering experiments
with pair distributionfunction analysis. The ratio of
different phases of iron oxide (wustite, magnetite and
maghemite)was obtained using X-ray absorptions spectroscopy.
The morphology of the particles wascharacterized using
scanning electron microscopy and small angle scattering. The
relationshipbetween the composition of the NPs and the
exchange bias effect is studied. Furthermore, themagnetic
properties of the samples can be tuned by oxidation or
reduction via differentannealing procedures. These results
provide important information for the manipulation of
theexchange bias in oxide NPs.},
month = {Mar},
date = {2022-03-14},
organization = {30th annual meeting of the German
Crystallographic Society (DGK), Ludwig
Maximilians Universität München +
online (Germany + online), 14 Mar 2022
- 17 Mar 2022},
cin = {JCNS-2 / PGI-4 / JARA-FIT},
cid = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
$I:(DE-82)080009_20140620$},
pnm = {632 - Materials – Quantum, Complex and Functional
Materials (POF4-632) / 6G4 - Jülich Centre for Neutron
Research (JCNS) (FZJ) (POF4-6G4)},
pid = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G4},
typ = {PUB:(DE-HGF)1},
url = {https://juser.fz-juelich.de/record/906825},
}