Magnetization enhancement and cation valences in nonstoichiometric (Mn,Fe)3-δO4 nanoparticles

We present a study of the structural and magnetic properties of (Mn,Fe)3-δO4 nanoparticles synthesized by soft mechanochemistry using Mn(OH)2 × 2 H2O and Fe(OH)3 powders as starting compounds. The resulting nanoparticles with a composition of the (Mn,Fe)3-δO4 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, Mössbauer 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, MS, of 73.5 emu/g at room temperature, is among the highest reported so far among nanocrystalline ferrite systems of similar composition.