Superparamagnetic MFe₂O₄ (M = Fe, Co, Mn) Nanoparticles: Tuning the Particle Size and Magnetic Properties through a Novel One-Step Coprecipitation Route

Abstract

Superparamagnetic ferrite nanoparticles (MFe 2 O 4 , where M = Fe, Co, Mn) were synthesized through a novel one-step aqueous coprecipitation method based on the use of a new type of alkaline agent: the alkanolamines isopropanolamine and diisopropanolamine. The role played by the bases on the particles' size, chemical composition, and magnetic properties was investigated and compared directly with the effect of the traditional inorganic base NaOH. The novel MFe 2 O 4 nanomaterials exhibited high colloidal stability, particle sizes in the range of 4−12 nm, and superparamagnetic properties. More remarkably, they presented smaller particle sizes (up to 6 times) and enhanced saturation magnetization (up to 1.3 times) relative to those prepared with NaOH. Furthermore, the nanomaterials exhibited improved magnetic properties when compared with nanoferrites of similar size synthesized by coprecipitation with other bases or by other methods reported in the literature. The alkanolamines were responsible for these achievements by acting both as alkaline agents and as complexing agents that controlled the particle size during the synthesis process and improved the spin rearrangement at the surface (thinner magnetic "dead" layers). These results open new horizons for the design of waterdispersible MFe 2 O 4 nanoparticles with tuned properties through a versatile and easily scalable coprecipitation route.

Large-Pore Mesoporous Ho3Fe5O12 Thin Films with a Strong Room-Temperature Perpendicular Magnetic Anisotropy by Sol–Gel Processing

“…This, however, is not unusual for nanomaterials and is often associated with surface spin canting and others size-related effects. [67][68][69] More importantly, the hysteresis curves confirm the magnetic easy axis as lying perpendicular to the film plane, as already indicated by the FC data. The "saturation" field is lower and the remanent magnetization and coercive fields are larger for the out-of-plane direction, which is particularly evident in the measurements at room temperature (the in-plane loop is significantly more skewed).…”

Magnetization and Specific Absorption Rate Studies of Ball-Milled Iron Oxide Nanoparticles for Biomedicine

“…As seen in Table 4 the maghemite sample has a higher saturation magnetization (37.50 emu/g) compared to that of magnetite (32.87 emu/g), opposite to expectation. This is attributed to the presence of nonstoichiometry and a thicker "dead layer" in the magnetite particles compared to those of maghemite [43]. Nonstoichiometry implies partial oxidation of magnetite to maghemite, as already observed in the Mössbauer spectra.…”

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“…This matches with the findings of Pereira et al [42] who found that saturation magnetization tends to decrease with decreasing particle size. Furthermore, there is something called digestion time which refers to the time one waits after the reaction temperature is reached before adding Oleic acid to the solution [37].…”

“…Furthermore, there is something called digestion time which refers to the time one waits after the reaction temperature is reached before adding Oleic acid to the solution [37]. Ayyapan et al [37] found that average particle size increased from 14 nm to 19 nm as the digestion time was increased from 1 min to 120 min whereas the saturation magnetization decreased (which again corresponds to the findings of Pereira et al [42] that decreasing particle size leads to decreasing saturation magnetization).…”