Magnetic-plasmonic core-shell nanomaterials offer a wide range of applications across science, engineering and biomedical disciplines. However, the ability to synthesize and understand magnetic-plasmonic core-shell nanoparticles with tunable sizes and shapes remains very limited. This work reports experimental and computational studies on the synthesis and properties of iron oxide-gold core-shell nanoparticles of three different shapes (sphere, popcorn and star) with controllable sizes (70 to 250 nm). The nanoparticles were synthesized via a seed-mediated growth method in which newly formed gold atoms were added onto gold-seeded iron oxide octahedrons to form gold shell. The evolution of the shell into different shapes was found to occur after the coalescence of gold seeds, which was achieved by controlling the amount of additive (silver nitrate) and reducing agent (ascorbic acid) in the growth solution. First principles calculation, together with experimental results, elucidated the intimate roles of thermodynamic and kinetic parameters in the shape-controlled synthesis. Both discrete dipole approximation calculation and experimental results showed that the nanopopcorns and nanostars exhibited red-shifted plasmon resonance compared with the nanospheres, with the nanostars giving multispectral feature. This research has made a great step further in manipulating and understanding magnetic-plasmonic hybrid nanostructures and will make important impact in many different fields.

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Nanofibers of cobalt manganese oxide (CoMn 2 O 4) were grown using an electrospun technique. Structural and microstructural characterizations confirm the formation of phase pure CoMn 2 O 4 with high porosity. The potential application of CoMn 2 O 4 nanofibers as an electrode material for energy storage device was studied using cyclic voltammetry and galvanostatic charge-discharge measurements. A specific capacitance of 121 F/g was observed with enhanced cyclic stability. Furthermore, an energy storage device was fabricated by sandwiching two electrodes separated by an ion transporting layer. The device showed a specific capacitance of 241 mF/cm 2 in 3M NaOH electrolyte. The effect of temperature on the charge storage properties of the device was also investigated for high temperature applications. The device showed about 75% improvement in the charge storage capacity when the temperature was increased from 10 to 70 o C.This research suggests that nanofibers of CoMn 2 O 4 could be used for fabrication of energy storage devices which could operate in a wide temperature range with improved efficiency.

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Pure phase exchange coupled nanocomposites of magnetically hard-soft oxides, (hard) SrFe12-yAlyO19 -(soft) x Wt.% Ni0.5Zn0.5Fe2O4 were prepared via one-pot autocombustion method. The hard-phase magnetic anisotropy was systematically varied via Al3+ doping and magnetic properties of the nanocomposites were assessed as a function of magnetic soft-phase content in the nanocomposite. As synthesized, ferrites were assessed for phase composition, crystallinity, and magnetic properties by using XRD and VSM respectively. Exchange coupling behavior was observed in nanocomposites for all soft phase content in the low field region up to 1200 Oe. Also, exchange coupling was observed to weaken with increase in Al3+ content in the hard phase of the composite. As a result of hard-soft exchange coupling, the saturation magnetization, reduced remanence, and Curie temperature were observed to be higher than those of pure SrFe12O19 hexaferrite. The present study is novel in its approach of tuning magnetic parameters of exchange-spring nanocomposites via systematically controlling magnetic parameters of the hard phase and content of the soft phase.