Faculty Publications
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Item Electrical and magnetic properties of chitosan-magnetite nanocomposites(2010) Bhatt, A.S.; Bhat, D.K.; Santosh, M.S.Magnetite powders in nanometer size have been synthesized by the hydrothermal process. Various magnetic films of chitosan and the synthesized magnetite nanopowders containing different concentrations of the latter were prepared by ultrasonication route. The X-ray diffraction (XRD) studies and the transmission electron microscopy (TEM) images showed that the synthesized magnetite particles had 80 nm dimensions. The band gap of the composites was evaluated using the UV-visible Spectroscopy. The influence of magnetite content on the magnetic properties of the composite showed a decrease in the saturation magnetization with the decrease in the magnetic content. The effect of magnetite content on the dielectric properties of the polymer film at different frequencies from 0.01 to 105 Hz was studied using an electrochemical impedance spectroscopy. The possible mechanism for the observed electrical properties of the composite films was discussed. © 2010 Elsevier B.V. All rights reserved.Item Crystallinity, conductivity, and magnetic properties of PVDF-Fe 3O4 composite films(2011) Bhatt, A.S.; Bhat, D.K.; Santosh, M.S.The formation of Fe3O4 nanoparticles by hydrothermal process has been studied. X-ray Diffraction measurements were carried out to distinguish between the phases formed during the synthesis. Using the synthesized Fe3O4 nanoparticles, poly(vinyledene fluoride)-Fe3O4 composite films were prepared by spin coating method. Scanning electron microscopy of the composite films showed the presence of Fe3O4 nanoparticles in the form of aggregates on the surface and inside of the porous polymer matrix. Differential Scanning calorimetry revealed that the crystallinity of PVDF decreased with the addition of Fe3O4. The conductitivity of the composite films was strongly influenced by the Fe3O4 content; conductivity increased with increase in Fe3O4 content. Vibration sample magnetometry results revealed the ferromagnetic behavior of the synthesized iron oxide nanoparticles with a Ms value of 74.50 emu/g. Also the presence of Fe3O4 nanoparticles rendered the composite films magnetic. © 2010 Wiley Periodicals, Inc.Item Microwave-assisted synthesis and magnetic studies of cobalt oxide nanoparticles(2011) Bhatt, A.S.; Bhat, D.K.; Tai, C.-W.; Santosh, M.S.An efficient microwave-assisted route has been used to synthesize nanoparticles of cobalt oxide. The particles were well characterized by transmission electron microscopy (TEM) which showed that the average diameter of the particles is around 6 nm. X-ray diffraction (XRD) studies further confirmed the formation of the spinel Co3O4. Purity of the products was detected by Fourier transform infrared spectroscopy (FTIR) combined with thermal gravimetric analysis (TG/DTG). The magnetic measurements revealed a small hysteresis loop at room temperature indicating a weak ferromagnetic nature of the synthesized Co3O4 nanoparticles. The magnetic moment of the particles was measured to be 4.27 ?eff. © 2010 Elsevier B.V. All rights reserved.Item Crystallinity, magnetic and electrochemical studies of PVDF/Co 3O4 polymer electrolyte(Elsevier Ltd, 2012) Bhatt, A.S.; Bhat, D.K.Organic-inorganic nanocomposites are gaining importance in the recent times as polymer electrolyte membranes. In the present work, composites were prepared by combining nano sized Co3O4 and poly(vinyledene fluoride) (PVDF), using spin coating technique. The surface of the PVDF/Co 3O4 system characterized through field emission scanning electron microscopy (FESEM) revealed a porous structure of the films. The nanoparticles tend to aggregate on the surface and inside the pores, leading to a decrease in the porosity with an increase in Co3O4 content. Co3O4 nanoparticles prohibit crystallization of the polymer. Differential scanning calorimetry (DSC) studies revealed a decrease in crystallinity of PVDF/Co3O4 system with an increase in the oxide content. Magnetic property studies of the composite films revealed that with an increase in Co3O4 content, the saturation magnetization values of the nanocomposites increased linearly, showing successful incorporation of the nanoparticles in the polymer matrix. Further, ionic conductivity of the composite films was evaluated from electrochemical impedance spectroscopy. Addition of Co3O4 nanoparticles enhanced the conductivity of PVDF/Co3O4 system. © 2011 Elsevier B.V. All rights reserved.Item Magnetic property and corrosion resistance of electrodeposited nanocrystalline iron-nickel alloys(Elsevier B.V., 2012) Pavithra, G.P.; Hegde, A.In the present investigation we have galvanostatically synthesized nanocrystalline Fe-Ni alloys on copper substrate. The effect of current density (c.d.) on composition, surface morphology and phase structure were studied for explaining the magnetic and electrochemical properties of the nanocrystalline alloy. The bath found to exhibit the preferential deposition of less noble Fe than Ni, and at no conditions of c.d., the deposition has changed from anomalous to normal type. Surface morphology and structural characteristics of the deposits were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. As composition of the alloy varied, consequent to the current density a change of body centered cubic structure (bcc) to face centered cubic structure (fcc) was observed for nanocrystalline materials. Finally, the conditions responsible for peak magnetic property and corrosion resistance were optimized. Factors responsible for improved functional properties were explained in terms of surface morphology and crystalline grain size of the coatings. © 2012 Elsevier B.V.Item Magnetic and dielectric properties of Fe3BO6 nanoplates prepared through self-combustion method(World Scientific Publishing Co. Pte Ltd wspc@wspc.com.sg, 2017) Kumari, K.In the present investigation, a facile synthesis method is explored involving a self-combustion of a solid precursor mixture of iron oxide Fe2O3 and boric acid (H3BO3) using camphor (C10H16O) as fuel in ambient air in order to form a single phase Fe3BO6 crystallites. X-ray diffraction (XRD), Field emission electron microscopy (FESEM), magnetic, and dielectric properties of as prepared sample are studied. From XRD pattern, a single phase compound is observed with an orthorhombic crystal structure (Pnma space group), with average crystallite size of 42 nm. A reasonably uniform size distribution of the plates and self-assemblies is retained in the sample. A magnetic transition is observed in dielectric permittivity (at ~445 K) and power loss (at ~435 K) when plotted against temperature. Aweak peak occurs near 330K due to the charge reordering in the sample. For temperatures above the transition temperature, a sharp increase of the dielectric loss is observed which occurs due to the presence of thermally activated charge carriers. A canted antiferromagnetic Fe3+ ordering in a Fe3BO6 lattice with a localized charge surface layer is an apparent source of exhibiting a ferroelectric feature in this unique example of a centrosymmetric compound. An induced spin current over the Fe sites thus could give rise to a polarization hysteresis loop. Due to the presence of both ferromagnetic as well as polarization ordering, Fe3BO6 behaves like a single phase multiferroic ceramics. © The Author(s).Item Electrical, dielectric and magnetic properties of Sn-doped hematite (?-SnxFe2-xO3) nanoplates synthesized by microwave-assisted method(Elsevier Ltd, 2018) Bindu, K.; Ajith, K.M.; Nagaraja, H.S.Hematite nanoparticles are of interest due to their exceptional electrical and magnetic behavior and various technological applications. The doping of hematite can vary its electrical and magnetic properties. Here, we report the effect of different concentrations of Tin doping on electrical, dielectric and magnetic properties of hematite synthesized by the microwave-assisted method. Tin-doped ?- Fe2O3 (?-SnxFe2-xO3) samples have been characterized using XRD, TGA, FESEM, and EDS (mapping). XRD pattern shows the rhombohedral structure of ?-SnxFe2-xO3. The synthesized samples have nanoplate like structure with a uniform distribution of tin throughout the sample. Electrical properties were investigated using dielectric and impedance studies. The dc resistivity and ac conductivity decreased with increase in concentration up to x = 0.06 (Sn0.06Fe1.94O3). However, it increased with further increase in the concentration of tin. The hopping of electrons between Fe3+ and Fe2+ in octahedral sites accounts for the observed conduction behavior. A single semi-circle of the cole-cole plot for ?-SnxFe2-xO3 indicates the dominant grain boundary effect in conduction. Dielectric constant and loss factor reveal the dielectric relaxation in ?-SnxFe2-xO3 samples. The magnetic properties were studied using VSM, which shows that ?-SnxFe2-xO3 are antiferromagnetic/weakly ferromagnetic in nature with high coercivity. © 2017 Elsevier B.V.Item Pyrolysis-controlled synthesis and magnetic properties of sol–gel electrospun nickel cobaltite nanostructures(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Kumar, B.S.; Dhanasekhar, C.; Adyam, A.; Kalpathy, S.K.; Anandhan, S.Nickel cobaltite (NCO) is a binary transition-metal oxide, which is extensively used as an electrocatalyst and magnetic material. NCO nanofibers and NCO/graphene composite exhibit high electrochemical reactivity due to the directional bridging of NCO particles. This makes NCO a promising candidate electrode material for use in supercapacitors and batteries. Besides, NCO is also a promising magnetic material due to its unique structural composition, where the cations are seated in octahedral sites surrounded by oxygen vacancies. In the present work, a simple and reliable method was discovered for tuning the morphological and structural changes of nickel cobaltite (NCO) nanoparticles, which were reshaped along the NCO nanofibers, by controlling the pyrolysis soaking time. As the pyrolysis soaking time increases, NCO transforms from inverse spinel to normal spinel; and the morphology of NCO nanoparticles changes from spherical to rod-like. These changes were validated by the hypsochromic peak shifts in Raman, and FTIR spectroscopies. The magnetic measurements reveal changes in the shape of the hysteresis loop, which are explained on the basis of structural and morphological changes in the nanostructure. The net magnetisation increases and coercivity decreases, with an increase in pyrolysis soaking time. These changes in magnetic parameters are attributed to structural changes caused by the formation of oxygen vacancies, and surface effects due to switching in morphology of the NCO nanoparticle. [Figure not available: see fulltext.]. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.