Cobalt driven enhancement of nanomagnetism in iron-oxide nanoparticles encapsulated in a synthetic ferritin shell

We have examined the effects of Co doping (0-12% relative to total metal) on the magnetic properties of iron-oxide nanoparticles incorporated in a synthetic ferritin shell. Mossbauer spectroscopy revealed that the nanoparticles consisted of a mixture of Fe3O4 and gamma-Fe2O3, and that Co was integrated exclusively into the B-sites of the Fe3O4 phase. Cobalt doping resulted in the formation of CoxFe3-xO4/gamma-Fe2O3 nanoparticles with x = 0, 0.25, 0.51, 0.56, and 0.63. Magnetometry and susceptometry experiments showed that substantial enhancements in the coercivities, blocking temperatures and anisotropy constants of the magnetoferritin nanoparticles occurred for all Co doping levels. Our results show that the Co altered significantly the local atomic Fe magnetism and enhanced the magnetic nanoparticle anisotropy considerably. (C) 2012 American Institute of Physics. [doi:10.1063/1.3678318]