Two-Component Magnetic Structure Of Iron Oxide Nanoparticles Mineralized In Listeria Innocua Protein Cages

Magnetometry was used to determine the magnetic properties of maghemite (gamma-Fe2O3) nanoparticles formed within Listeria innocua protein cage. The electron magnetic resonance spectrum shows the presence of at least two magnetization components. The magnetization curves are explained by a sum of two Langevin functions in which each filled protein cage contains both a large magnetic iron oxide core plus an amorphous surface consisting of small noncoupled iron oxide spin clusters. This model qualitatively explains the observed decrease in the temperature dependent saturation moment and removes an unrealistic temperature dependent increase in the particle moment often observed in nanoparticle magnetization measurements. (C) 2010 American Institute of Physics. [doi:10.1063/1.3400033]