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contributor.authorNayak, B B-
contributor.authorBahadur, D-
contributor.authorVitta, Satish-
identifier.citationMagnetic Nanocomposite Material, Doctoral Thesis Submitted to IIT Bombayen
descriptionCopyright for the thesis belongs to IIT Bombayen
description.abstractThe 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.extent6218844 bytes-
publisherIIT Bombayen
subjectMagnetic nanocompositeen
subjectColossal magnetoresistanceen
subjectChemical reductionen
subjectElectrical transporten
titleMagnetic Nanocomposite Materialen
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