Controlled phase evolution and the occurrence of single domain CoFe2O4 nanoparticles synthesized by PVA assisted sol-gel method

• Published in: Journal of magnetism and magnetic materials 2018-04, Vol.451, p.602-608
• Main Authors: Srinivasa Rao, K., Ranga Nayakulu, S.V., Chaitanya Varma, M., Choudary, G.S.V.R.K., Rao, K.H.
• Format: Article
• Language: English
• Subjects: Coercivity and single domain; Saturation magnetization; Spinel phase
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2017.11.069

•High saturation magnetization of 84.63 emu/g has been observed for a particle size of 8.1 nm.•Single domain to multidomain state has been established by dM/dH vs H and variation of coercvity with particle size.•Estimated single domain size (6.7 nm) matches well with observed particle size (6.5 nm) from TEM. The present investigation describes the development of cobalt ferrite nanoparticles having size less than 10 nm, by a sol-gel method using polyvinyl alcohol as chelating agent. X-ray results show all the samples, annealed above 700 °C have spinel structure. The information about phase evolution with reaction temperatures was obtained by subjecting the as-prepared powder for DSC/TGA study. High saturation magnetization of 84.63 emu/g has been observed for a particle size of 8.1 nm, a rare event reported till date. The dMdH versus H curves suggest that the transition from single domain state to multi-domain state occurs with increasing annealing temperature and the critical size for the single domain nature of CoFe2O4 is around 6.5 nm. The estimated critical diameter for single domain particle (6.7 nm) is in good agreement with that (6.5 nm) obtained from Transmission Electron Micrographs. The highest coercivity (1645 Oe) has been found for a particle of size 6.5 nm.