Low temperature and high magnetic field Mössbauer study of CuFe2O4 synthesized by sol–gel auto-combustion method

Abstract

Copper ferrite samples were prepared by sol–gel auto-combustion method and annealed from 400 to 800 °C. The structure and morphology of the samples was analyzed by x-ray diffraction and scanning electron microscopy techniques. An In-field Mössbauer spectroscopic analysis was carried out at a temperature of 5 K without and with 5 T magnetic field. A cubic phase with spinel ferrite structure was observed for the as prepared sample and the sample annealed at 400 °C. Further, a tetragonal copper ferrite phase along with CuO and α-Fe2O3 as secondary phases was identified for 500, 600, 700 and 800 °C annealed samples. The estimated average crystallite size was found to be in the range of 27–43 nm. The grain growth and the agglomerated morphology were observed due to annealing at higher temperatures. The Mössbauer analysis reveals that isomer shift values 0.347–0.534 mm/s, shows the random variation. S1 sextet (A-site) has a higher hyperfine field than S2 sextet (B-site). The larger variation of quadrupole shift for the observed sextets shows that crystal structure has lattice distortions. S1 sextet has a lower relative absorption area than S2 sextet, while the S3 sextet (α-Fe2O3) has an increasing relative absorption area as the annealing temperature rises. Inversion parameter values were found in the range of 0.51–0.88 at 5 K and 0.66–0.95 at 5 K–5 T. The partial inverse and random spinel nature of prepared samples was observed. The estimated weight percentage of the copper ferrite samples clearly indicates an increase in the α-Fe2O3 and CuO impurity phases. The evolution of structural phases and their impact on the cation distribution in copper ferrite were studied by Mössabuer spectra taken at low temperature and high magnetic field.