Mössbauer Studies on Nanocrystalline Diol Capped γ-Fe2O3

Nanocrystalline γ-Fe2O3 was prepared by refluxing ferric nitrate in 1,4-butanediol. Characterisation was done by XRD, FTIR and Raman spectroscopy. TEM showed that the average particle size of the two samples were 9 nm and 6 nm with a small particle size distribution. FTIR and TG showed that the γ-Fe2O3 particles were capped with the diol. Mossbauer spectra of the 6 nm sample showed that the sample is superparamagnetic with a blocking temperature around 225 K. With increase in particle size, blocking temperature increases. 20 K MS of 9 nm sample was fitted to 2 sextets. IS, QS and Hf parameters indicate presence of Fe3+ on A and B sites of the spinel lattice. MS of 6 nm sample were fitted to 3 sextets: Fe3+ ions on A and B sites and on the surface. As the coating is attached to the surface Fe3+ ions, EFG of these ions will be larger than the bulk Fe3+ ions. Hence the QS and Hf values are different for the 3rd sextet. These results indicate that although both the samples are nanocrystalline and both are coated, the effect of coating on the MS is only shown by the sample with smaller particle size. Thus when the particles are large the EFG of the Fe3+ ions in the bulk and surface are same and hence good fitting of the spectra can be obtained with 2 sextets only. From these results it may be concluded that synthesis of γ-Fe2O3 in diol results in a diol coated sample and the coating can be detected by MS when the particle size is very small.