Facile Synthesis of Monodisperse Maghemite and Ferrite Nanocrystals from Metal Powder and Octanoic Acid

Abstract

Extremely small, monodisperse, and spheric maghemite (γ-Fe2O3, 2–3 nm) and manganese (4–7 nm), cobalt (3–5 nm), and zinc ferrite (5–7 nm) nanocrystals are directly accessible on a large scale starting from inexpensive metal powders and octanoic acid by thermolysis in a high-boiling solvent. Bigger particle size is obtainable by prolonged reaction time according to the Ostwald ripening principle. The superparamagnetic nanocrystals and their assembly have been characterized by transmission electron microscopy, powder X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, and energy-dispersive X-ray spectroscopy.

Spin canting in ferrite nanoparticles

“…1a; δ = 0.37 mm/s, QS = 0.60 mm/s) are comparable to those observed for 11 nm nanostructured zinc ferrite prepared by high energy ball milling [6] and to 10 nm zinc ferrite NPs synthesized from ferric nitrate solution [7]. It can be concluded that the small particle sizes (3-7 nm, [3]) lead to a fast superparamagnetic relaxation resulting in doublets at room temperature. We attribute the observed deviations from lorentzian line shape to those particles, which do not relax faster than the Mössbauer time window of ∼10 −7 s. For MnFe 2 O 4 NPs a quadrupole splitting of 0.57 mm/s is observed (Fig.…”

“…For the sample with the smallest particle size (CoFe 2 O 4 , 3-5 nm [3], see Fig. 3c,f) the relative area of the spin-canting component is higher than in the two other samples (50 %) whereas the calculated canting angle is 59 • .…”

“…i = 0), could be seen in the 5 T spectrum, which would also explain the magnetic properties and the high saturation magnetization of the ZnFe 2 O 4 nanoparticles in ref. [3].…”

“…Highly crystalline manganese-, zinc-and cobalt-ferrite nanoparticles were synthesized as described in [3]. Mössbauer spectroscopy was performed in a setup as described in [4] with a closed-cycle helium cryostat (Cryo Industries of America, Inc.) equipped with a superconducting magnet with a maximal field of 5 T, oriented parallel to the γ -radiation.…”

“…A possibility to measure the amount of canted spins is Mössbauer spectroscopy with a large applied external field, in which the bulk ions' spins, but not the surface ions' spins align. In the following paper we present a study on zinc, manganese and cobalt ferrite nanoparticles which have been prepared by means of a new preparation route directly from metal powders and octanoic acid by thermolysis in a high-boiling solvent [3].…”