Probing interface and finite size effects in magnetic ferrite nanoparticles by electrochemical measurements

We determine the nanoparticle surface-charge density in electric double-layered magnetic fluids, based on different ferrite spinel-type particles with controlled mean sizes, by using electrochemical measurements. The results show that for large-size particles the surface is fully ionized whereas for smaller mean sizes, the saturated value of the superficial density of charge is significantly reduced. This decrease is analyzed taking into account that surface atoms of nanoscale particles present reduced coordination due to finite size and interface effects