Magnetization enhancement and cation valences in nonstoichiometric (Mn,Fe)(3-delta)O-4 nanoparticles

We present a study of the structural and magnetic properties of (Mn,Fe)(3-delta)O-4 nanoparticles synthesized by soft mechanochemistry using Mn(OH)(2) x 2 H2O and Fe(OH)(3) powders as starting compounds. The resulting nanoparticles with a composition of the (Mn,Fe)(3-delta)O-4 type are found to have a core/shell structure with different Mn/Fe ratios in the core and at the surface. XPS analysis points to valences of +2, +3, and +4 for Mn and +3 for Fe at the particle surface. Combined results of XRPD, Mossbauer spectroscopy, and EDX analysis suggest that there is a deviation from stoichiometry in the nanoparticle core compared to the shell, accompanied by creation of cation polyvalence and vacancies. The value of saturation magnetization, M-S, of 73.5 emu/g at room temperature, is among the highest reported so far among nanocrystalline ferrite systems of similar composition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700228