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CHAPTER 1
INTRODUCTION
Materials with features on the scale of nanometer often have properties dramatically different
from their bulk scale counterparts. Nanocrystalline materials are single phase or multiphase
polycrystals, the crystal size of which is of the order of few nanometers so that about 40 to 80
% of the atoms are in the grain boundaries . Nanostructure science and technology is a broad
and interdisciplinary area of research and development activity that has been growing
worldwide in the past decades. Important among these nanoscale materials are
nanocomposites, in which the constituents are mixed at nanometer length scale. They often
have properties that are different compared to conventional microscale composites and can be
synthesized using simple and inexpensive techniques. The study of nanocomposite materials
requires a multidisciplinary approach with impressive technological promise, involving novel
synthesis techniques and an understanding of physics and surface science .
During the last decade, the development of magnetic nanocomposite materials has been the
source of discovery of spectacular new phenomena, with potential applications in the fields of
information technology, telecommunication or medicine . Magnetic nanocomposite materials
are generally composed of ferromagnetic particles (grain size in nanometer scale) distributed
either in a non-magnetic or magnetic matrix . The shape, size and distribution of the magnetic
particles play an important role in determining the properties of such materials. The matrix
phase separates the magnetic particles and changes the magnetic exchange interaction. This
affects the transport and magnetic properties. Therefore, understanding and controlling the
structure of materials is essential to obtain desired physical properties.
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CHAPTER 2
BRIEF HISTORY
Nanocomposite magnetic materials have their origins in the amorphous alloys that were
brought to market in the 1970's. Amorphous materials are characterized by a lack of long
range atomic order, similar to that of the liquid state. Production techniques include rapid
quenching from the melt and physical vapor deposition is another. The lack of crystallinity
causes amorphous materials to have a very low magnetic anisotropy. METGLAS 2605™
Fe78Si13B9 is a common amorphous magnetic alloy, in which B acts as a glass forming
element. The importance of anisotropy suggests searching for other materials with isotropic
magnetic properties. In magnetic materials the ferromagnetic exchange length expresses the
characteristic distance over which a magnetic atom influences it's environment, and has
values on the order of 100 nm. If the magnet has a structure with grain diameters smaller than
the exchange length, it becomes possible to "average" the anisotropy of the grains to a low
bulk value. Such a material then realizes the high saturation magnetisation (Ms) of the
crystalline state and low coercivity (Hc) due to randomized anisotropy.
In 1988 Y.Yoshizawa developed the FINEMET™ alloy based on Fe73.5 Si13.5B9Nb3Cu1.
This was an extension of the common Fe-Si-B alloy with Cu as a nucleation agent and Nb as
a grain refiner. The material is produced in the amorphous state and then crystallized by
annealing. Nb that segregates to the grain boundaries acts a diffusion barrier preventing grain
growth. The structure is a nanocomposite of 10- 100 nm diameter bcc- FeSi grains embedded
in an amorphous intergranular matrix.
In 1990 K.Suzuki reported the development of the Fe88Zr7B4Cu1 alloy which was named
NANOPERM™. Zr and B act as glass forming agents in this alloy and the microstructure
consists of α-Fe grains embedded in an amorphous matrix. By eliminating Si, higher
saturation inductions are achieved than in FINEMET, but the Hc are also higher. The
amorphous intergranular phase in both FINEMET and NANOPERM have Curie temperatures
lower than that of the nanocrystalline grains.
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In 1998 M.A. Willard reported the development of HITPERM, an alloy based on the
composition Fe44Co44Zr7B4Cu1. The key distinction is the substitution of Co for Fe.
HITPERM forms α'- FeCo grains in a Co enriched amorphous matrix. The amorphous matrix
has a Curie temperature higher than the primary crystallization temperature of the alloy. This
allows the α'-FeCo grains to remain exchange coupled at high operating temperatures. Due to
the presence of Co, HITPERM alloy has an Ms higher than FINEMET or NANOPERM as
well as a higher Hc.
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CHAPTER 3
RECENT DEVELOPMENT AND UPDATED INFORMATION
In the field of magnetic nanocomposites,there has been a lot of progress in the preparation of
functional magnetic nanocomposites and hybrid materials. Some of the latest magnetic
nanocomposite materials will be briefly explained. The preparation methods , few properties
and applications will be explained in short since there are a lot of new and hybrid
materials.The main focus will be on the different types of the functional nanocomposites and
hybrid materials. There are a number of categories according to which functional
nanocomposites are classified. Some of them that will be dealt with are given below-
Core Shell type Multicomponent Magnetic Nanoparticles
Colloidal crystals
Mesoscale magnetic nanocomposites
Functional magnetic polymers
3.1 Multicomponent magnetic NPs: core–shell type NPs
The combination of two nanoscaled entities into a single hybrid particle has recently attracted
much attention due to the numerous possibilities of application. Hybrid NPs may provide a
platform with dual imaging capabilities for medical diagnosis (e.g., simultaneous magnetic
and optical imaging), dual action combining magnetic imaging and therapy, and multiplexing
in sensors. By this approach, the respective properties of the components may be combined
and optimized independently. In addition, cooperatively enhanced performances due to
collective interactions between the constituents have been achieved. Otherwise, however, the
direct combination of the different entities may lead to undesired effects such as
luminescence quenching by direct contact of magnetic NPs and quantum dots (QDs). To date,
several morphologies of multicomponent, magnetic hybrid NPs have been reported, including
core–shell and heterodimeric NPs.
The general strategy for multicomponent nanostructures is to first prepare NPs of one
material, and then use them as nucleation seeds to deposit the other material. This strategy
has been well established for the synthesis of semiconductor QDs with epitaxial shells, while
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the controlled synthesis of uniform NPs that combine materials with different
crystallographic structures, lattice dimensions, chemical stabilities and reactivities still faces
many challenges. To date, a number of heterostructures has been synthesized by applying a
seedmediated approach. Coating has been routinely applied for magnetic core stabilization
and surface functionalization in view of biomedical and technical applications.
One of the simplest methods for preparing core–shell type NPs has been the partial oxidation
of magnetic metal NPs to form a shell of the native oxide on the particle surface.
Polycrystalline Fe3O4 shells, e.g., which were generated by chemical oxidation on Fe
particles, were shown to successfully protect and stabilize Fe NPs against full oxidation.For
Co-CoO NPs, additionally to their stabilization, an exchange bias effect was observed as a
result of a strong interaction between the nanometre scale antiferromagnetic CoO layer and
the ferromagnetic Co core. Bimagnetic core–shell systems such as FePt-Fe3O4 or FePt-
CoFe2O4, where both core and shell are strongly magnetic (ferro- or ferrimagnetic), show
effective exchange coupling phenomena and facilitate the fabrication of magnetic materials
with tunable properties. The magnetic properties, e.g., magnetization and coercivity, can be
readily controlled by tuning the chemical composition and the geometrical parameters of the
core and the shell (Fig. 1).
Fig. 1 FePt-Fe3O4 NP assembly: (a) TEM image, (b) magnetization curve measured at 10 K
(Fe3O4 shell thickness 1 nm), and (c) normalized coercivity hc as a function of the Fe3O4
volume fraction.
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3.2 Colloidal crystals
The assembly of small building blocks (e.g., atoms, molecules, and NPs) into ordered
macroscopic superstructures has been an important issue in various areas of chemistry,
biology, and material science. Self-assembly of NPs into two-dimensional and three-
dimensional superlattices with a high degree of translational order has attracted a lot of
attention since the early observation of iron oxide super crystals by Bentzon.
More recently, self-assembled super crystals of iron oxide nanocubes by a drying-mediated
process, applying a magnetic field at the initial stage of the process was developed. These
super crystals did not only reveal a translational order but further an orientational order with a
crystallographic alignment of the nanocubes. The assembly of NPs of different materials into
defined colloidal crystals or quasi crystals provides a general path to a large variety of
composite materials (metamaterials) with new collective properties arising from the
interaction of the different Nanocrystals(NCs) in the assembly.
The formation of three-dimensionally ordered binary superlattices with a large structural
diversity, by combining two sets of NCs, e.g., magnetic NCs with semiconductor
QuantumDots(QDs) or metal particles was achieved. In a model system, PbSe semiconductor
QDs and superparamagnetic g-Fe2O3 NCs with independently tuneable optical and magnetic
properties were co-assembled by slow solvent evaporation.The PbSe NCs displayed a size-
dependent, near-infrared (NIR) absorption and emission, whereas the as-synthesized,
superparamagnetic g-Fe2O3 NCs revealed a weak absorption in the NIR at 1400 nm. It was
shown that electrical charges on sterically stabilized NCs determine the stoichiometry of the
superlattices together with entropic, van der Waals, steric and dipolar forces. The charge state
of the NCs could be tuned by adding small amounts of ligands, e.g., carboxylic acids, TOPO,
or dodecylamine. The addition of carboxylic acid to solutions of PbSe–Fe2O3 NC mixtures
resulted in the growth of AB or AB2 superlattices, whereas the addition of TOPO to the same
mixtures favoured growth of AB13 or AB5 structures (Fig. 2). The single domain regions of
the AB2 and AB13 superlattices ranged from 0.16 to 2 mm2. As there are a growing number
of monodisperse NC systems available, the use of NCs with independently tuneable
properties will enable the synthesis of divers materials with material responses which can be
fine-tuned to magnetic, electrical, optical, and mechanical stimuli.
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Fig. 2 TEM micrographs and sketches of AB13 superlattices of 11 nm g- Fe2O3 and 6 nm
PbSe NCs.
(a) Cubic subunit of the AB13 unit cell.
(b) AB13 unit cell built up of eight cubic subunits.
(c) Projection of a {100}SL plane at high magnification.
(d) As (c) but at a low magnification (inset: small-angle electron diffraction pattern).
(e) Depiction of a {100} plane.
(f) Projection of a {110}SL plane.
(g) As (f) but at a high magnification.
(h) Depiction of the projection of the {110} plane.
(i) Small-angle electron diffraction pattern.
(j) Wide-angle electron diffraction pattern of an AB13-superlattice .
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3.3 Mesoporous Magnetic Nanocomposites
A mesoporous material is a material containing pores with diameters between 2 and 50 nm.
In recent years, the synthesis of functional mesoporous magnetic microspheres with a defined
size and narrow size distribution has attracted increased attention as promising materials for
various applications. The following figure displays a typical four step procedure for the
synthesis of mesoporous superparamagnetic microspheres consisting of:
(1) Synthesis of superparamagnetic NPs .
(2) Development of a dense, nonporous SiO2 layer.
(3) Templated growth of the porous SiO2 shell.
(4) Template removal by calcination or solvent extraction.
The supermagnetic nanoparticles used was Fe3O4.Etching of the magnetic cores in harsh
media is typically prevented by introduction of an intermediate, nonporous SiO2 layer in step
(2). Particles (500 nm) with magnetic core and an ordered, mesoporous SiO2 shell with
perpendicular oriented accessible pores were obtained by such a four-step procedure using
cetyltrimethylammonium bromide (CTAB) as mesopore template. The template was finally
removed by extraction with acetone.
Schematic illustration of a typical four-step procedure for the synthesis of superparamagnetic
mesoporous SiO2 spheres.
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After obtaining Fe3O4-SiO2 particles, by adding other compounds, it can be used in various
Biomedical applications Some of them are given below-
The Fe3O4- SiO2 particles could be further loaded with fluorescing dyes (fluorescein
isothiocyanate (FITC) and rhodamine B isothiocyanate (RITC)) and doxorubicin
(DOX) and were tested for MR and fluorescence imaging as shown in figure (a).
(a) Uniform Fe3O4-SiO2 particles with a single Fe3O4 core
2-bromo-2-methylpropionic acid-modified Fe3O4 NPs were reacted with amine-
functionalized, dye-doped mesoporous SiO2 spheres.The pores of the nanocomposite
could be further loaded with the anti-cancer drug doxorubicin and thus served as a
multimodal platform for optical imaging, MR contrast enhancement, and drug
delivery.
(b) mesoporous SiO2 particles decorated with multiple Fe3O4 NPs
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3.4 Functional Magnetic Polymers
Polymer coatings have been formed on magnetic NPs to simply change the surface properties
of superparamagnetic NPs. The polymer then acts as a stabilizer or improves the
biocompatibility of the NPs. However, magnetic NPs are also able to couple their physical
properties with those of the polymer matrix. For example, magnetic NPs can be used to
transfer forces applied by an external magnetic field to a surrounding polymer matrix,
resulting in a change of shape or movement. This can be utilized for a variety of applications,
such as actuators, switches, or magnetic separation. Moreover, magnetic NPs have been
combined with polymer matrices which are sensitive to temperature changes induced by an
AC magnetic field. Inductive heating of thermoresponsive polymers has been exploited for
temperature- responsive flocculation of NPs, drug delivery, and shape transition
applications.The following two functional magnetic polymers will be explained further-
Au-shell NPs with amphiphilic diblock copolymers
Ferrogels
3.4.1 Au-Shell NPs with Amphiphilic Diblock Copolymers
Thermo-responsive γFe2O3-Au NPs have been prepared by using amphiphilic organic
diblock copolymer chains (Fig. 3).127 The diblock copolymer chains included a thermally
responsive poly- (N-isopropylacrylamide) (pNIPAAm) block and an amine-containing
poly(N,N-dimethylaminoethylacrylamide) (DMAEAm) block. An additional –C12H25
hydrocarbon tail drived the formation of micelles. The micelles were loaded with Fe(CO)5,
followed by subsequent thermolysis. The amine of the pDMAEAm block further served as
electron donor for reducing AuCl4_ to form a Au shell. Thermal aggregation of the particles
above their lower critical solution temperature leads to dielectric coupling and to changes in
the surface plasmon spectra.
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Fig. 3 Schematic illustration of the synthesis of magnetic-core, Au-shell NPs with
amphiphilic diblock copolymers.
3.4.2 Ferrogel
Matrix-dispersed composite materials of rather rigid polymer matrices filled with magnetic
particles, viz. magnetic elastomers or magnetoelasts, have been known for many years. These
materials are used as permanent magnets, magnetic cores, connecting and fixing elements in
many areas. They display a low flexibility and do not change their size, shape, and elastic
properties in the presence of an external magnetic field.
More recently, a new generation of magnetic elastomers, consisting of mainly nanosized,
superparamagnetic particles dispersed in a highly elastic polymer matrix, has attracted
increasing interest in basic research as well as in certain applications. ‘‘Smart’’ ferrogels
show unique magneto-elastic properties, i.e., they undergo a quickly controllable change in
shape upon exposure to a magnetic field. These peculiar magnetoelastic properties may be
used to create a wide range of motion and allow a smooth change in shape and movement.
Ferrogels are a promising class of materials for many applications, including actuators,
switches, artificial muscles, and drug delivery systems. Ferrogels usually consist of a
crosslinked polymer forming the gel matrix, and magnetic NPs dispersed in the matrix.
Owing to interactions between the NPs and the polymer chains, the incorporated magnetic
NPs connect the shape and physical properties of the gel to an external magnetic field.
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A ferrogel composed of crosslinked poly(N-tert-butylacrylamide-co-acrylamide) and Fe3O4
NPs, e.g., has been prepared by a two-step procedure.
First, the hydrogel was synthesized by free-radical crosslinking copolymerization of the
corresponding monomers, followed by subsequent co-precipitation of Fe2+ and Fe3+ in
alkaline medium. A cylinder of the ferrogel was placed in a nonuniform magnetic field
switching on and off, where the average magnetic field gradient was perpendicular to the axis
of the ferrogel. Fig. 4 shows the reversible bending process of this ferrofluid cylinder due to
the magnetic field.
Fig. 4 Bending process of a ferrogel cylinder due to a magnetic field
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3.5 Applications of Magnetic NanoComposites
The combination of nanotechnology and medicine has yielded a very promising offspring that
is bound to bring remarkable advance in fighting cancers. In particular, nanocomposite
materials based novel nanodevices with bi- or multi- clinical functions appeal more and more
attention as such nanodevices could realize comprehensive treatment for cancers. Because it
can provide an effective multimodality approach for fighting cancers, cancer comprehensive
treatment has been fully acknowledged. Among the broad spectrum of nano-biomaterials
under investigation for cancer comprehensive treatment, magnetic nanocomposite (MNC)
materials have gained significant attention due to their unique features which not present in
other materials. For instance, gene transfection, magnetic resonance imaging (MRI), drug
delivery, and magnetic mediated hyperthermia can be effectively enhanced or realized by the
use of magnetic nanoparticles (MNPs). Therefore, MNPs are currently believed with the
potential to revolutionize the current clinical diagnostic and therapeutic techniques.
3.5.1 Destruction of tumour cells by action of NanomagneticComposites
The treatment involves getting the nanoparticles inside the target cell, then applying a strong
enough magnetic field to orient them within the cell. Indeed, nanoMag nanoparticles have an
iron oxide core carrying a magnetic moment. During activation, the magnetic moments,
which were initial randomly oriented within the cell, line up with the external magnetic field,
transforming the magnetic energy into rotational kinetic energy. The forced orientation of
these particles throughout the period of exposure induces directional forces which strain the
cell. When the nanoparticle concentration is high enough within the cell, the tumour cell is
destroyed. Depending on the level of stress in the cell and/or the resulting damage, the
tumour cells enter into apoptosis or necrosis. When the field is switched off, the nanoparticles
adopt once again a random orientation and their anti-tumour activity ceases instantaneously.
Rotation Time-dependent binding of
Cell components
Action of nanoMag on tumour cells
Cell
Stress
s
Apoptosis
Necrosis
Cell
Stress
s
Repair & Survival
Apoptosis
Necrosis
Necrosis
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3.5.2 Transformers
Miniaturization and efficiency requirements demand the reduction of size and mass of core
materials in transformer. Increasing the Ms and μ will allow less magnetic material to be used
for a given transformer application. Decreasing Hc will reduce loss in AC applications,
improving efficiency. Operating temperatures may increase as power electronic systems
become more densely populated with components. This creates a need for magnetic materials
with increased operating temperatures. This can be achieved with nanocrystalline materials
with high crystalline and amorphous Tc to prevent particle decoupling.
3.5.3 DC-DC power converters
DC-DC power converters offer the advantage of reduced size and weight over conventional
line frequency transformer based power supplies. These converters are high frequency
devices that use magnetic transformers and inductors, along with active circuit elements, to
convert voltage levels. Ferrite materials are presently used to meet the frequency
requirements. The low Ms and Tc of ferrite materials limits the miniaturization potential of
converters. A magnetic material that had the Ms of iron and an operating frequency of 1 MHz
could result in a factor of 50 reduction in weight and volume. Nanocomposite magnetic
materials already have this Ms and have operating frequencies of 100 kHz. New, more
resistive nanocomposite structures have been conceived that will increase the operating
frequency above 1 MHz.
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CHAPTER 4
CONCLUSION
The field of Magnetic nanocomposites is indeed very vast and still growing at a very fast
pace.It has great advantages and applications as discussed in the previous chapters. As it is
small in size it has great advantages like higher surface area which can carry drugs to the
biological systems. Also because of the smallness in the size of the particles it can be
transported to various parts of the body and can be detected by advanced technological
systems.
On the other hand ,synthesis of high-quality magnetic nanoparticles in a controlled manner,
and detailed understanding of the synthetic mechanisms are still challenges to be faced in the
coming years. Synthesis of oxide or metallic magnetic nanoparticles often require the use of
toxic and/or expensive precursors, and the reaction is often performed in an organic phase at
high temperature at high dilution. These conditions to be maintained is a great challenge in
itself and the safety aspect of humans involved is to be considered.
One of the biggest challenges in biomedical applications of magnetic nanoparticles lies in
dealing with the issue of technology transfer. There are opportunities in this respect for more
interdisciplinary approaches, for example, to ensure that the laboratory based experiments
can more explicitly emulate the expected conditions that would be encountered in real life
situations. There is also scope for significant contributions via the mathematical modelling of
complex systems, with the objective of understanding more specifically the full gamut of
physical phenomena and effects that together determine whether, in the final analysis, a
given application will be successful.
Magnetic nanocomposites offer to open new vistas in the area of drug delivery and they
promise as a prudent tactic to overcome the drug delivery related problems when the
problems of toxicity,localization and cost are addressed. If once the safety and hazardous
aspects of the materials is clearly understood and overcome, this field will certainly offer
much more benefits to mankind than it has already done.
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CHAPTER 5
REFERENCES
Magnetic Nanocomposite Materials for High Temperature Applications by Frank
Johnson, Amy Hsaio, Colin Ashe, David Laughlin, David Lambeth, Michael E.
McHenry - Department of Materials Science and Engineering, Carnegie Mellon
University,Pittsburgh.
Magnetic Nanocomposite Materials by Bibhuthi Bhusan Nayak(Doctor of
philosophy).
Preparation of functional magnetic nanocomposites and hybrid materials:recent
progress and future directions.- Silke Behrens
Activatable Nanoparticles for Cancer Treatment. Nanobiotix by V. Simon, A.
Ceccaldi, and L. L´evy.