Nanotechnology has spurred efforts to design and produce nanoscale components for incorporation into devices. Magnetic nanoparticles are an important class of functional materials, possessing unique magnetic properties due to their reduced size (below 100 nm) with potential for use in devices with reduced dimensions. Recent advances in processing by chemical synthesis and the characterisation of magnetic nanoparticles are the focus of this review. Emphasis has been placed on the various solution chemistry techniques used to synthesise particles, including: precipitation, borohydride reduction, hydrothermal, reverse micelles, polyol, sol-gel, thermolysis, photolysis, sonolysis, multisynthesis processing and electrochemical techniques. The challenges and methods for examining the structural, morphological, and magnetic properties of these materials are described.

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Dopamine forms an initial structure coordinated to the surface of the iron oxide nanoparticle as a result of improved orbital overlap of the five-membered ring and a reduced steric environment of the iron complex. However, through transfer of electrons to the iron cations on the surface and rearrangement of the oxidized dopamine, a semiquinone is formed. Because of free protons in the system, oxygens on the surface are protonated, which allows for the Fe2+ to be released into the solution as a hydroxide. This released fragment of the nanoparticle will then eventually oxidize in air to a form of an iron(III) oxyhydroxide. All of the reported results demonstrate that the reactivity between Fe3+ and dopamine quickly facilitates the degradation of the nanoparticles. The energetic modeling studies substantiate our proposed decomposition mechanism and thus conclude that the use of dopamine as a robust anchor for iron oxide or iron oxide shell particles will not fulfill the need for stable ferrofluids in most biomedical applications.

We present theoretical and experimental studies that explain the observed strong enhancement of the magneto-optical (MO) Faraday rotation in all-metal core-shell Co-Ag nanoparticles (NPs) attributed to localized surface plasmon resonance (LSPR). We also explain why the optical absorption and MO spectra peaks appear blue-shifted with increased Co core size while keeping the NP size constant. Further, we demonstrate direct correlation between the strong LSPR induced electromagnetic fields and the enhanced MO activity of the NPs.

We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties.

This paper discusses the relationship between synthesis conditions, crystal morphology, and theoretical modeling of copper and nickel nanoparticles prepared by a modified polyol process. The polyol serves as a solvent, a reducing agent, and a capping agent, and we investigate the role several polyol types play in the nucleation and growth of metallic nanoparticles. The nanoparticles are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Our results demonstrate that changing the solvent system from a short chain polyol (ethylene glycol) to a long chain polyol (tetraethylene glycol) greatly affects the resulting morphology of copper nanoparticles. These results suggest that the polyol is playing a major role as an in situ capping agent and that the various polyol chain lengths in-turn result in various particle morphologies by directly altering the nucleation and growth steps. We were also able to use theoretical modeling to investigate the mechanism for growth to better understand the intermediate structure stability. This work presents an alternative approach in investigating the polyol mechanism by using both theoretical and experimental results and opens new insight for the synthesis of metals and alloys by the polyol process.

A low-temperature topotactic route is used to assemble metal-anion arrays within a perovskite host. Ion exchange between RbLaNb 2 O 7 and CuX 2 (X ) Cl, Br) results in a new set of layered copperoxyhalide perovskites, (CuX)LaNb 2 O 7 . Rietveld structural analysis of X-ray powder diffraction data confirms the formation of a two-dimensional copper-halide network in the double-layered perovskite interlayer. This new structure type contains unusual CuO 2 X 4 octahedra that corner-share with NbO 6 octahedra from the perovskite slab and edge-share with each other along all four equatorial edges. Magnetic susceptibility measurements show that both products exhibit antiferromagnetic transitions below 40 K. Additionally, these materials are found to be low-temperature phases, decomposing completely by 700°C. The synthetic approach described in this work is significant in that it demonstrates how host structures can be used as templates in the directed low-temperature assembly of extended metal-anion arrays.

The antisymmetric stretching band of the ν3 vibration of azide ion was studied in nanosize water droplets confined in reverse micelles by Fourier transform infrared spectroscopy. In reverse micelles of nonionic nonylphenyl polyoxyethylene (NP) and cationic cetyltrimethylammonium bromide (CTAB), the ν3 stretching frequency of the azide ion is red-shifted compared to in bulk water, whereas in anionic reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), it is blue-shifted. The shifts at ω ) 3 (ω ) [H2O]/[surfactant]) for NP, CTAB, and AOT reverse micelles are -14, -31, and +4 cm -1 , respectively. In all cases, the shift decreases as ω is increased, indicating that the water interior approaches the properties of bulk water. This agrees with the changes observed in the IR spectra of water and the surfactant headgroup in NP reverse micelles as a function of ω. Comparison between reverse micelles formed with different surfactants reveals that the ν3 azide band is sensitive to its local environment, which could be affected by interactions with the surfactant headgroups, the solvating water properties, and the presence of counterions. In addition, the aggregation number of NP reverse micelles in cyclohexane was obtained via time-resolved fluorescence quenching. The radius of the water droplet in the interior of micelle was found to increase from 13 to 34 Å for ω ) 3 to 10.