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Thesis (Doctor of Philosophy) >
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http://hdl.handle.net/2080/565
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| DC Field | Value | Language |
|---|
| contributor.author | Nayak, B B | - |
| contributor.author | Bahadur, D | - |
| contributor.author | Vitta, Satish | - |
| date.accessioned | 2007-12-07T08:00:57Z | - |
| date.available | 2007-12-07T08:00:57Z | - |
| date.issued | 2006 | - |
| identifier.citation | Magnetic Nanocomposite Material, Doctoral Thesis Submitted to IIT Bombay | en |
| identifier.uri | http://hdl.handle.net/2080/565 | - |
| description | Copyright for the thesis belongs to IIT Bombay | en |
| description.abstract | The present work deals with synthesis of composite materials consisting of magnetic
nanoparticles dispersed in a magnetic or nonmagnetic insulating matrix and a study of their
transport and magnetic properties. Two types of composites: ceramic–ceramic and metal–
ceramic have been synthesized using three different techniques, microwave refluxing, glassceramic
and aqueous reduction. These techniques promote formation of composites at the
nano level, which is one of the primary aims of this thesis. These techniques are highly
versatile and can be used for the synthesis of a wide variety of materials. Moreover, synthesis
of nanocomposites using these techniques has not been investigated in detail earlier and this
forms the objective in using these techniques.
In ceramic–ceramic system, the main magnetic material is manganite with a perovskite
type structure. The manganites are of interest because they exhibit colossal magnetoresistance
(CMR) behavior and enhancing the magnitude of CMR is of significant interest. Two
different combinations of composites: magnetic phase distributed in magnetic or nonmagnetic
matrix have been synthesized.
In the magnetic–magnetic ceramic system, the work describes the structural, transport
and magnetic properties of nanocrystalline CMR oxide, La0.67Ca0.33MnO3 (LCMO) and their
distribution in a magnetic insulating NiFe2O4 (NF) matrix synthesized using microwave
refluxing. The structural, transport and magnetic properties are found to depend strongly on
the Mn4+ concentration, grain size, pH of the precursor solution and the annealing temperature.
In the magnetic–nonmagnetic system, the work describes the structural, transport and
magnetic properties of LCMO distributed in an insulating nonmagnetic silicate or borate
matrix synthesized using glass-ceramic route. Selection of glass composition and effect of
nucleating agents are the important factors for making nanocomposites using this technique.
The CMR property of LCMO is found to vanish in the case of LCMO/NF nanocomposites
with increasing NF content while isolation of LCMO by SiO2 or borate based glass leads to
loss of CMR behavior. These results clearly show that both magnetic and transport properties
depend on interactions between LCMO grains.
In metal–ceramic nanocomposite system, Ni: NiO/ZrO2 nanocomposite materials have
been studied in detail. Different size and shapes (spherical, cylindrical, ellipsoid, hexagonal
and polyhedral) of Ni nanoparticles with a core-shell structure have been synthesized by
chemical reduction using sodium borohydride as a reducing agent. Crystalline Ni varying in
size from 2 nm to 26 nm distributed in a non-magnetic matrix of NiO/ZrO2 has been prepared
at room temperature by controlling the time of reaction and addition of Zr-salt solution of
different concentrations. The crystalline Ni clusters are found to be ferromagnetic at room
temperature with a well defined hysteresis and coercivity. The absolute resistivity of the
annealed samples (in H2 atmosphere) decreases up to x ≤ 0.10 (where x is the molar
concentration of Zr-salt) and then increases with the concentration of Zr-salt. These results are
in agreement with the microstructural results, which show that initially the addition of Zr-salt
promotes Ni formation leading to a better inter-particle connectivity. For x > 0.10, the interparticle
connectivity is reduced due to ZrO2 encapsulation and hence results in an increase in
resistivity. The microstructural results together with the transport and magnetic properties of
the nanoparticle system clearly show the potential of this technique to obtain size controlled
property tuning. | en |
| format.extent | 6218844 bytes | - |
| format.mimetype | application/pdf | - |
| language.iso | en | - |
| publisher | IIT Bombay | en |
| subject | Magnetic nanocomposite | en |
| subject | Colossal magnetoresistance | en |
| subject | Nanoparticle | en |
| subject | Microwave | en |
| subject | Glass-ceramic | en |
| subject | Chemical reduction | en |
| subject | Electrical transport | en |
| subject | Magnetetoresistance | en |
| title | Magnetic Nanocomposite Material | en |
| type | Thesis | en |
| Appears in Collections: | Thesis (Doctor of Philosophy)
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| File |
Description |
Size | Format |
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| Thesis_Bibhuti B Nayak.pdf | | 6073Kb | Adobe PDF | View/Open |
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