Iron oxide nanocrystals have size-dependent structures and magnetic properties that are useful in a host of applications, ranging from water purification to biomedical applications. For example, very small nanocrystals have tetrahedrally coordinated iron vacancies on their surfaces that may enhance arsenite adsorption. They also have size- and structure- dependent magnetic properties. Despite these attractive properties, questions remain regarding the influence of size on local atomic structure and magnetic properties in small (&lt; 10 nm diameter) iron oxide.  Here we describe studies of a series of 13 distinct sizes of spinel iron oxide nanocrystals spanning a range of 4-9 nm, all synthesized under the same conditions using a new continuous growth synthesis. The only synthetic parameter that changes the size of the particles is the amount of precursor added:  The solvent, surfactant and reaction temperature are the same for every size. As a consequence, these nanocrystals are nearly ideal for evaluating the size dependent properties and structure at this lengthscale. Magnetic measurements show that the saturation magnetization increases with size throughout the range.  Further, the calculated magnetic size is essentially the same as the physical size, suggesting that nearly all the iron within the nanocrystal contributes to the magnetism.  Detailed structural studies using Pair Distribution Function (PDF) analysis of total x-ray scattering measurements were carried out to probe the atomic-scale structure within these nanocrystals.  These studies reveal size-dependent nanoscale structural features, including differences in tetrahedrally and octahedrally coordinated iron vacancies in the lattice.<br/>

New insights regarding the local atomic structure and magnetic properties in sub-10 nm iron oxide nanocrystals produced by a living growth process

256th National Meeting (2018)

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