Biomedical Engineering Reference
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Fig. 9.3 Fe@ferrite MNPs .( a ) New synthetic route. The size of the Fe core is increased by
elevating the reaction temperature. The core is then overcoated with a ferrite shell. To further
enhance the particle magnetization, the shell is metal doped. ( b ) TEM image of Fe@ferrite MNPs.
Fe MNPs ( dotted circles ) were preserved during the coating process. ( c ) Fe@ferrite MNPs showed
stable magnetic properties over time with small changes (<10 %) in saturation magnetization .M s /.
( d ) The field-dependent magnetization (M)ofFe@MFe 2 O 4 MNPs at 300 K showed an unusual
feature: negligible remanent moments but the presence of hysteresis (Adopted from [ 42 ]. Copyright
2011 John Wiley and Sons, Inc.)
Ferrite-shell overcoat. Native Fe MNPs undergo rapid oxidation, which neces-
sitates the presence of protective shells. To prepare such shells, we carried
out the reaction for ferrite synthesis in the presence of as-prepared Fe MNPs,
based on the hypothesis that Fe MNPs could serve as nucleation sites for ferrite
formation. Indeed, the resulting particles (Fe@ferrite, Fig. 9.3 b) had Fe cores
whose sizes were similar to that of the initial Fe MNPs (dashed circles in
Fig. 9.3 b). Importantly, Fe@ferrite MNPs maintained their shape and magnetic
properties over time (Fig. 9.3 c), verifying the sturdy protection against oxidation
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