Cation distribution and particle size effect on Raman spectrum of CoFe2O4

Mössbauer and Raman spectroscopic studies were carried out on CoFe2O4 particles synthesized with size ranging from 6 to 500 nm (bulk). Cation distribution studies were carried out on the high temperature and room temperature phases of the microcrystalline CoFe2O4 by Mössbauer and Raman spectroscopic methods. The high temperature phase of CoFe2O4 showed a decreased inversion parameter of 0.69 as compared to the value of the room temperature phase of 0.95, indicating that the structure gradually transforms towards a normal spinel. Corresponding Raman spectra for these two phases of CoFe2O4 showed a change in relative peak intensity of the vibrational mode at 695 cm−1(A1g(1)) to 624 cm−1 (A1g(2)). The relative peak intensity ratio, Iv between the A1g(1) and A1g(2) vibrational mode was decreasing with lowering of inversion parameter of the CoFe2O4 spinel system. A variation of laser power on the sample surface was reflected in the cation distribution in ferrite phase. Superparamagnetic, single domain CoFe2O4 particles (6 nm) showed a 20 cm−1 red shift and broadening of phonon modes when compared to the macro-crystalline CoFe2O4 (500 nm). Variation of Raman shift with particle size was studied by considering the bond polarization model. Raman spectroscopic studies clearly indicate the variation in the cation distribution in nano-sized particles and distribution tending to a normal spinel structural configuration.