Magnetism of sol-gel fabricated CoFe2O4∕SiO2 nanocomposites

Abstract

Details of synthesis and characterization of sol-gel-produced CoFe2O4 nanoparticles embedded in the amorphous SiO2 matrix are presented together with results of an extended magnetization study of these materials. The particle size was found to increase from 6to15nm by varying the temperature of a subsequent annealing from 800to1100°C. All samples exhibited superparamagnetic behavior with values of the blocking temperature TB increasing with the particle size. At temperatures above TB the magnetization curves follow the expected Langevin scaling of M vs H∕T, which is consistent with the formation of the superparamagnetic state. For T<TB, the coercivity field Hc was found to be proportional to T and the frequency-dependent ac susceptibility was found to obey the Néel–Arrhenius law. Both observations are compatible with a model of noninteracting randomly oriented single-domain particles.

Luminescence and Amplified Stimulated Emission in CdSe–ZnS‐Nanocrystal‐Doped TiO2 and ZrO2 Waveguides

“…The zirconia sol was prepared in a similar manner to that used by Urlacher et al, by mixing Zr(OPr) 4 (1 mL, 2.26 mmol), acetylacetone (acac) (0.23 mL, 2.26 mmol), and i-PrOH (6 mL) [52]. The titania sol was prepared in a very similar fashion by mixing Ti(OPr) 4 (0.64 mL, 2.26 mmol), acac (0.23 mL, 2.26 mmol), and i-PrOH (6.4 mL).…”

“…The transfer of nanocrystals (NCs) into sol-gel-based matrices provides a generic pathway for the development of complex materials with unique optical, [1,2] electronic, [3] or magnetic [4,5] signatures. Of particular interest at present is the possibility that NC-doped glasses could provide stable laser media with tunable emission wavelengths.…”

Effect of the Silica Cover on the Properties of Co 3 O 4 Nanoparticles

“…The silica cover of the nanoparticles is usually prepared by the Stöber method [24,43,45]. This type of synthesis allows the oxidation of metals particularly cobalt [46].…”

A Magnetic Composite for Cleaning of Oil Spills on Water

“…For instance, removal of the polymer material from the water surface must be simple and easy (requiring low polymer densities, for floating on the water surface, and strong magnetic force, for possible use of magnets for removal of the polymer beads/sheets from the water surface) and the chemical affinity with the oil must be high (for maximum removal of oil from the aqueous environment). Both properties can be achieved through preparation of magnetic alkyd composites, as magnetic nanoparticles frequently present strong superparamagnetism [11,12] and alkyd resins usually present low densities, when compared to water. [13] Among the possible magnetic nanofillers used for preparation of the polymer composites, maghemite (gFe 2 O 3 ) is probably the most studied one, due to its very high superparamagnetic force, lower density (when compared to other magnetic fillers), and easiness of preparation.…”