Aging Investigation of Cobalt Ferrite Nanoparticles in Low pH Magnetic Fluid

Abstract

In this study, we report on how surface-passivated and nonpassivated cobalt ferrite nanoparticles (8 nm diameter), suspended as ionic magnetic fluids and aged under low pH conditions, revealed different behavior as far as the time evolution of the iron/cobalt cation distribution, crystal quality, coercivity, and saturation magnetization are concerned. Different techniques were used to perform a detailed study regarding the chemical stability, structural stability, and surface and magnetic properties of the suspended nanoparticles as a function of the aging time. Properties of surface-passivated and nonpassivated nanoparticles were investigated by transmission electron microscopy, X-ray diffraction, atomic absorption spectrometry, magnetic measurements, Raman spectroscopy, and Mössbauer spectroscopy. Our data showed that the employed nanoparticle surface passivation process, besides the formation of an iron-rich surface layer, modifies the nanoparticle core as well, improving the crystal quality while modifying the Fe/Co cation distribution and the nanoparticle dissolution rate profile. Magnetic data showed that the saturation magnetization increases for surface-passivated nanoparticles in comparison to the nonpassivated ones, though coercivity decreases after passivation. These two observations were associated to changes in the cation distribution among the available tetrahedral and octahedral sites.

Magnetite nanoparticles as-prepared and dispersed in Copaiba oil: study using magnetic measurements and Mössbauer spectroscopy

“…2). Our experimental findings are in very good agreement with the literature, as molecular surface passivation of nanosized cubic ferrite-based particles enhances the saturation magnetization values while improving the nanoparticle's crystalline quality [6].…”

Magnetic hyperthermia investigation of cobalt ferrite nanoparticles: Comparison between experiment, linear response theory, and dynamic hysteresis simulations

“…22,[27][28][29][30] On the other hand, a possible restriction to the use of some ferrites, including cobaltferrite, has to do with its potential toxicity caused by the leaching of Co atoms from the nanoparticle surface under biological environments. 22,31 Nevertheless, if such issues can be controlled, as for instance through an efficient surface passivation, this system could be interesting, especially at the non-linear regime (high magnetic fields), 6 where a larger magnetic anisotropy is expected to play a significant role. In this work, we show measurements of the specific absorption rate ((SAR); power dissipated per unit mass) as a function of particle size, saturation magnetization, coercive field, and magnetic anisotropy.…”

Ferrofluids: Synthetic Strategies, Stabilization, Physicochemical Features, Characterization, and Applications

“…[151] The saturation magnetization for surface-passivated NPs increased relative to the nonpassivated ones, though the coercivity decreased after passivation as a result of a modified cation distribution profile. When the particles move as a result of Brownian motion in polar carrier liquids such as water or ethylene glycol, the MNPs are stabilized rather by the introduction of surface charges.…”