Electron magnetic resonance of iron oxide nanoparticles mineralized in protein cages

Magnetic and structural properties determined by electron magnetic resonance (EMR) spectroscopy are reported for maghemite (γ-Fe2O3) nanoparticles formed through template-constrained mineralization within three protein cages with nominal diameters of 5, 8, and 24 nm. EMR spectra, obtained at 4.0, 9.2, 34.6, 94.9, and 130.0 GHz, and at ambient temperature, show dramatic frequency dependent effects in the line shapes, line-widths, and resonance-field shifts. Simulations of the spectra are used to obtain moment distribution parameters, which are consistent with size limitations imposed by the protein cages, but which reflect significant departures from bulk magnetization properties.