Size dependent magnetic properties of maghemite nanoparticles: a proposed project for neutron scattering investigations

Kelly Pisane (West Virginia University)

Nanoparticles, with large magnetic moments that can be manipulated with an external magnetic field, have potential uses in medicine because their sizes are comparable to biological scales. For such applications it is important to understand how their magnetic properties are affected by their size and size distribution. For this purpose, maghemite (γ-Fe₂O₃) nanoparticles with average diameters of 7.0 ± 0.8 nm, 6.3 ± 0.6 nm, 3.4 ± 0.8 nm and 2.5 ± 0.7 nm were synthesized and the structural properties were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Detailed ac and dc magnetic characterization of these nanoparticles is presented and discussed in terms of a distribution of particle sizes and magnetic moments. Key results discussed will include the development of an equation to describe the size dependence of the effective anisotropy constant for maghemite nanoparticles, the derivation of a relationship between two parameters used to discuss interparticle interactions, and the first theoretical basis for the commonly-used cutoff value for the model-independent interparticle interaction parameter. Experimental verification of both relationships will be presented using published data.

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