Cation Migration-Induced Crystal Phase Transformation in Copper Ferrite Nanoparticles and Their Magnetic Property

Abstract

Impact of crystal phase evolution on structural and magnetic properties of copper ferrite nanoparticles is studied and reported. The copper ferrite nanoparticles were synthesized by starch-assisted sol-gel auto-combustion method and further annealed at 200, 500, 800, and 1100°C. The X-ray diffraction study indicated phase evolution from cubic to tetragonal with increase of annealing temperature. Raman spectroscopy and Fourier transform infrared spectroscopy study revealed the impact of phase transformation and cation redistribution in copper ferrite nanoparticles with increase of annealing temperature. X-ray photoelectron study revealed the cation migration with annealing temperature, which is responsible for structural phase evolution. The field emission-scanning electron microscopy (FE-SEM) study revealed that the ferrite nanoparticles at a lower annealing temperature (200, 500, and 800°C) were agglomerated spherical and elongated particles in the grain size range 10–100 nm. However, at a higher annealing temperature (1100°C), it was hexagonal plate-like particles in the grain size range 50–200 nm. The increase in saturation magnetization (Ms) from 11.60 emu/g (200°C) to 25.48 emu/g (1100°C) with grain growth and crystal phase evolution (i.e., increase of c/a ratio and cation redistribution in CuFe2O4 mixed spinel ferrite) was noticed. In addition, a crystal phase evolution from cubic to tetragonal and a grain growth as a function of annealing temperature both cause also an increase in coercivity (Hc) value from 132.56 Oe (200 °C) to 1442.50 Oe (800 °C) Furthermore, the decrease of coercivity (Hc) value from 1442.50 Oe (800°C) to 218.06 Oe (1100°C) with increase of annealing temperature was due to the “pinning” effect of domain wall at the grain boundary.