Structural investigations and magnetic properties of cobalt ferrite nanoparticles prepared by sol–gel auto combustion method

Morphological and magnetic characteristics of cobalt ferrite nanoparticles synthesized by sol–gel auto combustion method using nitrates of respective metal ions have been studied. X-ray diffraction pattern was indexed by a Rietveld program to calculate accurate unit cell dimension. A Transmission Electron Microscope (TEM) confirmed the formation of single phase cobalt ferrite nanoparticles in the range 11–40 nm depending on the annealing temperature and time. The size of the particles increases with annealing temperature and time while the coercivity goes through a maximum, peaking at around 25 nm. A very large coercivity (10.2 kOe) is observed on cooling down to 77 K while typical blocking effects are observed below about 260 K. The high field moment is observed to be small for smaller particles and approaches the bulk value for large particles. Mossbauer spectra recorded at room temperature is a sextet indicating that there is a strong magnetic coupling and increase in sintering temperature from 570 ∘C to 800 ∘C do not affect Mossbauer parameters.