Cation distribution and particle size effect on Raman spectrum of CoFe 2O 4

Abstract

Mössbauer and Raman spectroscopic studies were carried out on CoFe 2O 4 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 CoFe 2O 4 by Mössbauer and Raman spectroscopic methods. The high temperature phase of CoFe 2O 4 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 CoFe 2O 4 showed a change in relative peak intensity of the vibrational mode at 695 cm −1( A 1g(1)) to 624 cm −1 ( A 1g(2)). The relative peak intensity ratio, I v between the A 1g(1) and A 1g(2) vibrational mode was decreasing with lowering of inversion parameter of the CoFe 2O 4 spinel system. A variation of laser power on the sample surface was reflected in the cation distribution in ferrite phase. Superparamagnetic, single domain CoFe 2O 4 particles (6 nm) showed a 20 cm −1 red shift and broadening of phonon modes when compared to the macro-crystalline CoFe 2O 4 (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.