(357a) Characterization Methods for Magnetic Nanoparticle Systems

Magnetic characterization of thin film and bulk materials is well-established and -understood. To date, this knowledge and their techniques have been directly transferred onto the characterization of nanoparticles. Unfortunately, due to the fundamental differences in material behavior on the nanoscale, these characterization methods are often inadequate to quantitatively characterize nanoparticles, either as individuals or as collections. Our goal is to develop the fundamental measurement methods for quantifying the parameters of interest in magnetic nanoparticles. Amongst these parameters are the blocking temperature, anisotropy, interactions, and distributions of coercivity and interactions. For example, three alternative methods for measuring the blocking temperature will be presented that remove the ambiguity inherent in the ?conventional? method (i.e. the peak position in the zero field cool magnetization vs. temperature measurement). First Order Reversal Curves (FORC) magnetometry is a technique being developed to quantify the interaction strength as well as the distribution in properties for a nanoparticle system. This model can be checked directly through small angle neutron scattering (SANS), although this technique is limited by available beam time and polydispersity of the nanoparticle system. Finally, measurement methods for determining both individual and collective anisotropy of nanoparticle systems using a combination of dispersion methods, temperature, and magnetic field in vector magnetometry will be presented. Each of the techniques will be described, along with initial experiments on cobalt and magnetite nanoparticle systems to demonstrate the information they can reveal.