Biomedical Engineering Reference
In-Depth Information
measured with ZFC and FC of the two nanostructures measured at an applied
fi eld of 10 Oe has been reported. Magnetite shows, in the ZFC curve, a visible
magnetic transition at 119 K; this corresponds to the Vervey transition that origi-
nates from a fast electron hopping process between Fe
3+
and Fe
2+
ions in the B
site of the ferrite [138]. The Vervey transition is peculiar to the magnetite phase,
and the fact that it is not observed in the ZFC curve of maghemite further confi rms
the Raman data - that is, that the two tube-in-tube structures are formed by pure
maghemite and magnetite phases. The coercivity at 300 K was 210 and 170 Oe,
and the saturation magnetization 90 and 70 emu g
− 1
(for the magnetite and
maghemite structures, respectively). The measured values of
M
s
were only a little
lower with respect to the bulk values, indicating the absence of any magnetic
disorder in these nanostructures. These results show great promise for the applica-
tion of these tube-in-tube structures in different fi elds, ranging from catalysis to
drug delivery [23] .
12.5
Conclusions and Perspectives
In this chapter, based on the experimental results described in Section 12.4, we
have attempted to outline the interplay between the magnetic properties and the
chemical composition, structure and morphology of magnetic nanostructured iron
oxides.
We have endeavored to illustrate that preparation methods have a relevant infl u-
ence - which is often undervalued - on such parameters. In fact, on the basis of
recently devised chemical preparation methods, our understanding of magnetic
behavior at the nanoscale has made remarkable progress in the past few years.
These improvements in synthetic methods derive mainly from: (i) the ability to
combine two or more classical methods (e.g., sol-gel and autocombustion, thermal
decomposition and coprecipitation); and (ii) the use of surfactants and complex
organic molecules, such as liquid crystals. This has led not only to the control of
particle size and size distribution, but also more recently to the use of soluble
templates in the fabrication of 1-D nanostructures and microstructures. Such
structures are capable of binding reversibly to nanocrystals so as to produce
organic-inorganic structures with size and shape specifi cities that can serve as
hybrid building blocks in aggregation-based pathways of crystal growth.
It has been shown how shape anisotropy-by modifying magnetic anisot-
ropy - can alter the magnetic behavior of these materials. Clearly, in the foreseeable
future, organic chemistry and biochemistry will take on a fundamental role in the
creation of 1-D, 2-D and 3-D ordered magnetic nanostructures. Moreover, as the
need for organic and biological molecules in the assembly of such complex struc-
tures becomes apparent, biochemists, organic and inorganic chemists will need
to share their talents. The result may be a series of well-ordered magnetic nano-
materials which, when assembled into nanodevices, might be used to control and
perform highly sophisticated functions.
