Biomedical Engineering Reference
In-Depth Information
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
