Surface effects in maghemite nanoparticles

A consistent model is presented for the variation of saturation magnetization with particle size in maghemite nanoparticles, based on the existence of a magnetically disordered layer with a constant thickness of 1 nm. For particles smaller than 3 nm, layer thickness increases rapidly, and M_S is already zero for 2.5 nm particle size. Magnetization measurements have been performed on maghemite–polymer nanocomposites with low size dispersion and a regular distribution of particles in the matrix. A representative number of samples have been studied with a diameter size in the range from 1.5 to 15 nm and ±10% of size dispersion.