Tuning a Colloidal Synthesis to Control Co²⁺ Doping in Ferrite Nanocrystals

Abstract

Cobalt-ferrite nanocrystals were synthesized using a high-temperature organometallic decomposition scheme in the presence of surfactant molecules. The influence of the addition of cosurfactant molecules of polyol type on the resulting nanocrystals was examined. The properties of the nanocrystals were studied using electron microscopy, and magneto-optical and Raman spectroscopies. The addition of the cosurfactants was found to influence the growth mechanism of the nanocrystals, resulting in a significant reduction in the concentration of the Co 2+ ions incorporated into the ferrite lattice up to a factor of 4 and an increase in the size of the synthesized nanocrystals. In addition, control over the occupation of octahedral versus tetrahedral coordination sites by the cobalt ions was demonstrated.

Influence of cobalt doping on the hyperthermic efficiency of magnetite nanoparticles

“…For instance, Barron et al [26] performed a systematic investigation of the parameters involved in this synthesis and reported a constant Co reduction throughout the whole investigated composition range (0.15 rx r1.0). Shemer et al [27] attributed the Co depletion to the presence of the long chain diol, HDD, although we did not observe any difference when the reaction was repeated without this surfactant (Table 1). In addition, a statistical study on the synthesis of cobalt ferrite by thermal decomposition reaction identified the decrease of the reflux temperature as responsible for the reduction of the Co:Fe ratio, suggesting that the decomposition of the Co-precursor occurs at higher temperature than the Fe precursor [28].…”

“…However, using OA, OAM and HDD as surfactants, we found that the Co:Fe ratio, determined by ICP-AES, was always lower than the nominal value, and, even by adding an excess of Co(acac) 2 while keeping the total moles of metal (Fe þCo) unchanged, samples with x 40.6 could not be obtained. A systematic Co depletion in Co x Fe 3 À x O 4 NPs synthesized by thermal decomposition of metal acetylacetonate precursors was already reported in the literature [26][27][28]. For instance, Barron et al [26] performed a systematic investigation of the parameters involved in this synthesis and reported a constant Co reduction throughout the whole investigated composition range (0.15 rx r1.0).…”

Preparation of iron cobaltite thin films by RF magnetron sputtering

“…Two peaks at high Raman shifts F 2g (3) (640 cm −1 ) and A 1g (695 cm −1 ) are assigned to the vibrations of cations and oxygen ions in Td sites [36,[38][39][40]. Three peaks at low Raman shifts F 2g (1) (185 cm −1 ) F 2g (2) (325 cm −1 ) E g (490 cm −1 ) are attributed to the vibrations of cations and oxygen ions in Oh sites [38][39][40].…”

Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol–gel process

“…Magnetic spinels of the Fe 3 O 4 and MFe 2 O 4 type have been successfully produced by various methods ranging from mechanical to gas phase and solution routes [9][10][11][12]. The latter include co-precipitation, thermal decomposition, hydro-and solvothermal, and reverse micelle approaches [13][14][15][16][17][18][19][20][21][22][23][24][25]. Whereas co-precipitation is particularly suitable for biological applications due to the formation of nanoparticles in aqueous media, thermal decomposition or hydrothermal methods are good alternatives in terms of precise morphology control.…”