The influence of the transition metal substitution on chemically prepared ferrite nanoparticles - Mossbauer studies

Mossbauer measurements were carried out in order to study the influence of the transition metal substitution TM/Fe (where TM Co, Ni, Mn, and (TM)(x)Fe3-xO4) ranging from 0.1 to 0.9 on the morphology and magnetic properties of ferrite nanoparticles. Chemically prepared magnetite nanoparticles with 13 nm were used as a reference material. The Mossbauer spectrum of the initial magnetite sample show a well-resolved magnetically split patterns connected with tetrahedral (A) positions and octahedral (B) positions. For low concentrations of TM, the relative intensities of the sextet that comes from the iron B position decrease. This means that the Co, Ni, Mn atoms are located preferentially in the B-site of the magnetite. However, the qualitative analysis of the spectra also suggests that Mn and Ni partially occupy the A-site. The increase of the concentration of the substitution transition metal causes broadening of the magnetic part of the spectra and appearance of a doublet in the central part of spectra for all samples. TEM studies show that the incorporation of the Me atoms into the structure causes a decrease of the average particle size. This is also confirmed by XRD. This also means that the blocking temperature decreases and for about Ni/Fe = 0.8 and TM/Fe = 0.9 (for Mn and Co) reaches room temperature. In the case of the nominal 0.9 substitution by Ni, a pure superparamagnetic state is observed, while for Co and Mn some of the particles are still below the blocking temperature, in agreement with the TEM studies. (C) 2012 Elsevier B.V. All rights reserved.