Microstructure and Magnetic Properties of Iron Oxide Nanoparticles Prepared by Wet Chemical Method

Abstract

The magnetic properties of iron oxide nanoparticles prepared by the chemical decomposition of the iron chlorides with the ratio Fe 3+ /Fe 2+ = 2.25 were studied by means of transmission electron microscopy, X-ray diffraction and Mössbauer spectroscopy in-and without external magnetic field. The transmission electron microscopy studies show that the nanoparticles have spherical shape with diameter about 13 nm. The transmission electron microscopy and X-ray diffraction patterns are composed of lines that could be indexed within the cubic spinel structure. The room temperature Mössbauer spectrum shows the coexistence of the broad magnetically split part and superparamagnetic doublet. The in-field Mössbauer measurements carried out in the temperature range from room temperature down to 13 K show a gradual increase in the spin canting on the surface of the nanoparticles and decrease in the intensity of the superparamagnetic doublet. The sample was subjected to annealing process performed at elevated temperature in air atmosphere in order to change the microstructure of the nanoparticles and in consequence to change the magnetic properties of the sample. The annealing process leads to the decrease in the value of quadrupole splitting of the superparamagnetic doublets.

Preparation and Characterization of Magnetic Nanoparticles

“…Changes observed as increase of central doublet intensity in comparison to sextet contribution can be a result of both. Such modifications of the spectra due to interparticle interaction were observed earlier [4,5].…”

Study of the surface chemistry and morphology of single walled carbon nanotube–magnetite composites

“…The central portion contribution was readily associated with the phenomenon of superparamagnetic relaxation related to the small particles size of the cores of the capped magnetite nanoparticles. In this regard, for magnetite, it has been reported that the particle size limit to observe the superparamagnetic behavior should be less than 10 nm [54,74]. Therefore, about 11% of the synthesized nanoparticles had particle diameter less than 10 nm, since, as shown in Table 2, the superparamagentic doublet was fitted with an isomer shift (d) of 0.354 mm/s, a quadrupole splitting (D) of 0.682 mm/s, with a relative abundance (R.A.) accounting for 11.2% of the total spectrum.…”

“…Therefore, the superparamagnetic relaxation should be observed as a single line, i.e., without quadrupole splitting. Thereafter, the observed splitting effect can be only justified on account of the presence of part of the 57 Fe atoms in the surface of the nanoparticles, because of the high specific surface of these nanoparticles (see Table 1), where the broken cubic symmetry causes that these atoms are immersed in a non-zero electric field gradient [74], producing quadrupole splitting. These iron cations located in the surface are essentially Lewis sites [52,59].…”

Synthesis of Zn2+ substituted maghemite nanoparticles and investigation of their structural and magnetic properties

“…This could be due to an increase in the number of iron ions on the surface of the nanoparticles compared to those located in inner of the nanoparticles. In fact, Fe ions on the surface cause deviation from cubic symmetry and then a non-zero electric field gradient [38]. The isomer shift and the quadrupole splitting of these components are around 0.35 mm/s which are in the range of Fe 3+ ionic state for maghemite nanoparticle.…”