Particle size effect on Mössbauer parameters in γ-Fe2O3 nanoparticles

Nanoparticles of maghemite (γ-Fe2O3) were synthesized by chemical co-precipitation method for different particle size ranges and Mössbauer spectroscopy was employed to see the particle size effect on the Mössbauer parameters, especially on the average internal magnetic field of the system. It was observed that the internal magnetic field increased with increase in particle size. The contribution of superparamagnetic component for all size ranges is almost equal, i.e. 10%, while the relaxed subspectrum contributes around 50% at all stages. The superparamagnetic component was a quadrupole doublet up to 40 nm and then it transformed into a singlet at larger particle sizes. This indicates that the electric field gradient vanishes for this particular Fe environment and has an ideal cubic symmetry.