Profound Interfacial Effects in CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4 Core/Shell Nanoparticles

Abstract

Two sets of core/shell magnetic nanoparticles, CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4, with a fixed diameter of the core (~ 4.1 and ~ 6.3 nm for the former and latter sets, respectively) and thickness of shells up to 2.5 nm were synthesized from metal chlorides in a diethylene glycol solution. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, and magnetic measurements. The analysis of the results of magnetic measurements shows that coating of magnetic nanoparticles with the shells results in two simultaneous effects: first, it modifies the parameters of the core-shell interface, and second, it makes the particles acquire combined features of the core and the shell. The first effect becomes especially prominent when the parameters of core and shell strongly differ from each other. The results obtained are useful for optimizing and tailoring the parameters of core/shell spinel ferrite magnetic nanoparticles for their use in various technological and biomedical applications.

Magnetic Properties of Fe3O4/CoFe2O4 Composite Nanoparticles with Core/Shell Architecture

“…According to the results of electron microscopy research, the average size of Fe 3 O 4 magnetic nanoparticles was about 6.3 nm [8]. As the effective thickness of the CoFe 2 O 4 shell increased, the average particle size also increased in accordance with the results of preliminary calculations.…”

“…The results of X-ray diffraction studies of the synthesized nanostructures were analyzed in work [8] in detail. All synthesized specimens had a cubic spinel structure (ICDD 19-0629) and were absolutely free of any impurity phases.…”

“…For the Fe 3 O 4 and CoFe 2 O 4 nanoparticles, the saturation magnetization amounted to 77 and 50 A m 2 /kg, respectively, at the temperature = = 5 K. It is worth noting that the corresponding values of s for the bulk specimens equaled 98 and 94 A m 2 /kg, respectively, [15]. The reduced magnetization of nanoparticles can be a result of the appreciable contribution from near-surface layers, which are characterized, as a rule, by a larger magnetic disorder [8]. A conclusion can also be drawn that the contribution of near-surface layers to the nanoparticle magnetization is larger in the CoFe 2 O 4 magnetic nanoparticles than in the Fe 3 O 4 ones.…”

“…Then they were mixed with diethylene glycol, and the solution was stirred for 1 h. Simultaneously, the solution of NaOH in DEG was prepared. The alkaline solution was added dropwise to the former solution, and the mixture was stirred again for 1 h. The obtained reaction mixture was heated up to a temperature of 200 ∘ C at a rate of 2-3 ∘ C/min and kept at this temperature for 1.5 h. The synthesis allowed us to fabricate Fe 3 O 4 and CoFe 2 O 4 magnetic nanoparticles with average sizes of about 6.3 and 4.1 nm, respectively, [8]. The synthesized Fe 3 O 4 and CoFe 2 O 4 nanoparticles in the form of their solutions in diethylene glycol were used to prepare mixtures of Fe 3 O 4 and CoFe 2 O 4 nanoparticles with the mass ratios between the components corresponding to the mass ratios between the core and shell materials in each core/shell specimen.…”

“…Currently, there are only a few studies in this direction [3,[8][9][10][11]. Issues giving rise to a full understanding of the influence of the core/shell architecture on the magnetization and the effective anisotropy of magnetic nanoparticles, as well as the role of interface effects in the formation of magnetic properties of composite nanostructures of this type, still remain open.…”