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Synthesis of CoFe2O4 Nanoparticles via the Ferrihydrite Route

Published online by Cambridge University Press:  18 March 2011

A. Manivannan ,
A. M. Constantinescu  and
M. S. Seehra
A. Manivannan
Affiliation:
Physics Department, West Virginia University, Morgantown, WV 26506-6315
A. M. Constantinescu
Affiliation:
Physics Department, West Virginia University, Morgantown, WV 26506-6315
M. S. Seehra
Affiliation:
Physics Department, West Virginia University, Morgantown, WV 26506-6315
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Abstract

Nanoparticles of CoFe2O4 in the size range of 5 nm to 36 nm have been synthesized by first producing two-line Co-doped ferrihydrite and annealing it at temperatures between 573 and 1073 K. Co-doped ferrihydrite is produced by reacting appropriate amounts of FeCl3/CoCl2 solutions with NH4OH at pH = 7. Thermogravimetric measurements provide evidence for the ferrihydrite to CoFe2O4 conversion between 500 and 700 K and x-ray diffraction is used to confirm the transformation to CoFeO4 and determine the particle size. The lattice constant increases initially with the increase in particle size approaching a constant value above 20 nm. The measured Tc equals 788 K for the 36 nm particles. Measurements of magnetization as a function of temperature and magnetic field confirm that the precursor Co-ferrihydrite is a superparamagnet with T ≃ 40 K, whereas for the 30 nm CoFe2O4, the coercivity Hc ≃ 7 kOe at 20 K, decreasing to Hc ≃ 800 Oe with Ms ≃ 60 emu/g at 300 K.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 658: Symposium GG – Solid-State Chemistry of Inorganic Materials III , 2000 , GG6.32
Copyright
Copyright © Materials Research Society 2001

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