Abstract
Nano crystalline cobalt ferrite CoFe2O4 powders were synthesized using the coprecipitation method. The effect of the calcination temperature and the Fe3+/Co2+ molar ratio on the phase formation, macro and microstructure and magnetic properties was studied systematically. The Fe3+/Co2+ was controlled to equal 2 and 2.75 while the annealing temperature (Ta) was adjusted to vary from 600 to 1000Co. the obtained powders were investigated using x-ray diffraction (XRD) analysis, Field emission scanning electron microscope (FESEM), Fourir transformation infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). For both the Fe3+/Co2+ ratios, the XRD results indicat the formation of well crystallized cubic spinel cobalt ferrite phase for the precursors annealed at 600Co up to 1000Co. However a second rhombohedral hematite phase whose content varies respectively from 3% and 15% was formed as the Fe3+/Co2+ varied from 2 to 2.75 at Ta=800 and 1000Co. The crystallite size (Dβ) as determined applying the win-fit program was found also to decrease from 54.5 to 48.6nm accompanied by an increase of the root mean square strain < eg>. Using Rditveld analysis no effect on the value of the lattice parameter (a) was detected. The FESEM micrographs reveal the formation of highly agglomerated particles for Fe3+/Co2+ =2.75 and Ta =1000Co. The FTIR analysis confirm the formation of the spinel structure phase for both Fe3+/Co2+ ratios at 1000Co, however the absorption bands shift to higher frequencies for Fe3+/Co2+ =2.75. Other bands at 1663 and 3472cm-1 ascribed to free or absorbed water molecules were also detected for this ratio. The Fe3+/Co2+ molar ratio was found to have a significant effect on the magnetic properties of the produced cobalt ferrite. The calculated magnetic parameters: the saturation magnetization (MS= 71.219emu/g), the coricivity (HC= 1443.8Oe) and the remanence ratio (Mr/MS= 0.405) were recorded to decrease as the Fe3+/Co2+ increases except for the curie temperature (TC) which increase from 405 to 410Co.
Highlights
Metal-oxide nanoparticles have been the subject of much interest because of their unusual optical, electronic and magnetic properties, which often differ from the bulk.Spinels of the type A2+B3+2O4 such as ZnFe2O4, MnFe2O4, NiFe2O4 and CoFe2O4 have attracted considerable attentions due to their broad applications in several technological fields including electronic devices, ferrofluids, magnetic drug delivery, microwave devices and high-density information storage [1,2,3,4]
In order to produce nanocrystallites with higher crystallinity and bigger particle size, the as prepared CoFe2O4 and Co0.8Fe2.2O4 nanocrystals were calcinated at different temperatures 600Co, 800Co and Structural studies means to detect the locations of the atoms in the unit cell while microstructural means to find the American Journal of Physics and Applications 2015; 3(2): 33-38 crystallite size, strain and type of defects
x-ray diffraction (XRD) study of CoFe2O4 sintered by conventional ceramic method confirmed the presence of 13.1% hematite residual phas[25]
Summary
Metal-oxide nanoparticles have been the subject of much interest because of their unusual optical, electronic and magnetic properties, which often differ from the bulk. Spinels of the type A2+B3+2O4 such as ZnFe2O4, MnFe2O4, NiFe2O4 and CoFe2O4 have attracted considerable attentions due to their broad applications in several technological fields including electronic devices, ferrofluids, magnetic drug delivery, microwave devices and high-density information storage [1,2,3,4]. Many preparation methods for CoFe2O4 nanoparticles have been quite involved requiring special techniques to prevent agglomeration [18] or microwave assisted synthesis [19]. Among these synthesis methods are: the wet chemical coprecipitation[20], microwave irradiation in polyol media[21], sol-gel auto-combustion[22], poly ethylene glycol-assisted hydrothermal method[23], mechanical milling and subsequent annealing[24] etc----. The effect of the Fe3+/Co2+ ratio and annealing temperature on the phase formation and crystallinity on the magnetic parameters were carefully studid
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