Size dependent strain and nanomagnetism in CoFe₂O₄ nanoparticles

The objective of this work is to investigate strain and magnetism at the nano scale in CoFe₂O₄ nanoparticles. CoFe₂O₄ nanoparticles of controlled size were synthesized using a chemical co-precipitation method at different reaction temperatures and molar concentrations of reagents without using any surfactant. Size dependent strain, structural, optical, morphological and magnetic properties of CoFe₂O₄ nanoparticles were investigated. Particle size was calculated by size distribution curve using FESEM images. It was observed that structural orientation and characteristic features of the strain are dependent on CoFe₂O₄ particle size. The formation of CoFe₂O₄ nanoparticles was confirmed by XRD, FESEM, Raman and FTIR spectroscopy. The good correlation between XRD analysis and Raman study was observed with the help of Raman shift (cm⁻¹) as a function of uniform and non-uniform strain curves for all sizes of CoFe₂O₄ nanoparticles. The size-dependent superparamagnetic properties of CoFe₂O₄ nanoparticles were studied systematically. The blocking temperature, coercivity and saturation magnetization increase on increasing the size of the CoFe₂O₄ nanoparticles was observed. Blocking temperature is a maximum temperature, above which the exchange bias does not occur. The size of the CoFe₂O₄ nanoparticles estimated from blocking temperature measurements correlated well with FESEM and XRD measurements. These CoFe₂O₄ nanoparticles have potential applications in gas sensors operating in hazardous environments.