Structure of manganese zinc ferrite spinel nanoparticles prepared with co-precipitation in reversed microemulsions

Abstract

The structure of Mn 0.5 Zn 0.5 Fe 2 O 4 spinel ferrite nanoparticles is studied as a function of their size and the experimental conditions of their synthesis using X-ray absorption spectroscopy. The nanoparticles of different sizes down to approximately 2 nm and with a narrow size distribution were synthesized using co-precipitation in reverse microemulsions. Simultaneous refinement of the X-ray absorption fine structure (EXAFS) of three constituting metals shows a migration of Mn and Zn ions to the octahedral site of the spinel lattice compensated by the corresponding migration of the Fe ions. To a smaller extent, Mn ions switch the occupation site already in bulk and in larger nanoparticles, while a sporadic migration of Zn is detected only in the nanoparticles with sizes below approximately 5 nm. X-ray absorption near edge structure (XANES) reveals considerable variations in the position of the Mn K edge, suggesting the average Mn valence in the nanoparticles to be higher than 3?. Annealing at 500°C relaxes the structure of as-synthesized nanoparticles toward the structure of the ceramic bulk standard.

Influence of synthesis method on structural and magnetic properties of cobalt ferrite nanoparticles

“…As shown in the case of Zn-ferrite (Makovec and Drofenik 2008;Makovec et al 2009), the spinel nanoparticles can sustain large deviations from their stoichiometry without losing their single-phase nature. When the nanoparticles TD were heated in air to 600°C, Fe 2 O 3 was precipitated, whereas the nanoparticles CP and ME remained in the single spinel phase after heating.…”

“…During annealing, the nanoparticles retained their single-phase spinel structure while they coarsened to reach particle size over 60 nm. It is known that the structure of nanoparticles relaxes toward the structure of the bulk at such high temperatures (Makovec and Drofenik 2008;Makovec et al 2009). For EXAFS, the Co-ferrite samples were intimately mixed with BN and pressed into thin pellets with a total absorption thickness of about 2 above the Fe and Co K-absorption edge (7,112 and 7,709 eV, respectively).…”

“…In the case of nanoparticles, the structure can substantially deviate from the bulk. The flexibility of the crystal structure is particularly pronounced in the spinel ferrite nanoparticles (Sato et al 1990;Kamiyama et al 1992;Jeyadevan et al 1994;Hamdeh et al 1997;Ammar et al 2004;Makovec and Drofenik 2008;Carpenter et al 1999;Calvin et al 2002;Makovec et al 2009;Morrison et al 2004;Li et al 2000;Sivakumar et al 2007;Tirosh et al 2006). For example, ZnFe 2 O 4 shows paramagnetic behavior as bulk material due to its normal spinel structure, with Zn ions incorporated almost exclusively at tetrahedral sites.…”

Investigating the Role of Shell Thickness and Field Cooling on Saturation Magnetization and Its Temperature Dependence in Fe3O4/γ-Fe2O3 Core/Shell Nanoparticles

“…However, the surface atoms experience a different environment than those on the core of the particle. The surface magnetization is controlled by several parameters such as atomic vacancies, change in atomic coordination, dangling bonds, and lattice disorder [9][10][11][12][13][14][15][16][17][18][19][20][21]. These parameters result in disordered surface spins.…”

Synthesis, investigation on structural and electrical properties of cobalt doped Mn–Zn ferrite nanocrystalline powders

“…Ferrites can be represented by the chemical formula of AB 2 O 4 , where A and B denote metal cations at tetrahedral (A) and octahedral (B) sites, respectively. The magnetic properties of the spinel ferrite materials originate from the antiferromagnetic coupling between the octahedral and tetrahedral sublattices [5].…”