Abstract
Cobalt ferrite (CoFe2O4) nanoparticles synthesized by chemical co-precipitation method were studied to see the effect of annealing temperatures on the structural parameters and magnetic properties of the sample. X-ray powder diffraction (XRD), transmission electron microscope (TEM) and SAD pattern demonstrated that single face (fcc) spinel structure of CoFe2O4 has been formed showing particles in completely crystalline state which was further confirmed by the lattice parameter and the unmixed hkl values. The particle size is in the range of about 5-10 nm depending on the annealing temperature from 200°C to 400°C. The grain growth occurred monotonically with the increase of annealing temperature. The magnetic properties demonstrated a strong dependence on particle size. The saturation magnetization Ms, remanent ratio Mr/Ms and coercivity Hc increased with the increase of particle size. The hysteresis curves for samples of different grain size showed the ferrimagnetic behavior which is completely analogous to the slow relaxation sextet peaks of Mössbauer spectroscopy. Other parameters such as chemical shift, quadruple splitting and hyperfine field and site occupancy of Fe3+ were determined by Mössbauer spectroscopy. Ferrimagnetic to superparamagnetic transition temperature known as blocking temperature TB was determined from the temperature dependent magnetization curves. With the increase of grain size, Blocking temperature also increases. Maximum entropy changes due to magnetic phase transition were also observed for mentioned annealing temperatures in the context of Magnetocaloric effect.
Highlights
In recent days, nanocrystalline ferrites become a subject of fascination because of their overwhelming application in human life as well as research areas
The structural, magnetic and magnetocaloric effect at various annealing conditions is studied here for Cobalt ferrite nanoparticles synthesized by Chemical co-precipitation method
The X-ray powder diffraction (XRD) study confirmed the formation of the single phase cubic spinel structure and the particle size are 5-10nm at different annealing temperature
Summary
Nanocrystalline ferrites become a subject of fascination because of their overwhelming application in human life as well as research areas. Iron-oxide nanoparticles have been used as an important specimen in the field of research and practical life on account of their unusual physical, electronic and magnetic properties compared to their bulk counterparts. With the reduction of particle size into nanoscale, some of these properties change drastically.[1,2,3,4,5] Complex relationship between nanostructural features and the macroscopic magnetic properties are not same for all combinations. To know the applications of a combination of ferrite, it is mandatory to inspect this relationship properly.[6]. Nanocrystalline ferrites have outstanding applications like magnetically guided drug delivery, magnetic
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