Effect of the Support on the Formation of FeCo Alloy Nanoparticles in an SBA-16 Mesoporous Silica Matrix: An X-ray Absorption Spectroscopy Study

A series of nanocomposites consisting of FeCo alloy nanoparticles supported on a three-dimensional cubic mesoporous silica matrix (SBA-16) were prepared by wet impregnation of the matrix with a solution of Fe and Co nitrates. FeCo alloy nanoparticles were obtained by heat treatment at 800 °C in reducing atmosphere of the impregnated SBA-16 previously calcined at 500 °C. Three different SBA-16 types were used as a support of the nanophase. The influence of the matrix on the absorption of Fe and Co ions was investigated using X-ray diffraction and X-ray absorption spectroscopy. In particular, extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at the Fe and Co K-edges were used in order to identify the intermediate products before reduction and to study the formation of the bcc FeCo alloy, which cannot be assessed unambiguously using X-ray diffraction. An important influence of the matrix has been observed in the phases formed before reduction, in the size of nanoparticles, and in the oxidation of the FeCo alloy nanoparticles

EDS, HRTEM/STEM, and X‑ray Absorption Spectroscopy Studies of Co-Substituted Maghemite Nanoparticles

A detailed study of the composition and structure of Co-doped maghemite nanoparticles with systematically varying composition has been carried out by transmission electron microscopy (TEM) techniques, such as high-resolution TEM, scanning TEM, and energy-dispersive X-ray spectrometry, and by X-ray absorption spectroscopy at the Fe and Co K-edges, analyzing both the extended X-ray absorption fine structure and the X-ray absorption near-edge structure regions. The latter techniques, in particular, allow us to determine the degree of inversion of divalent and trivalent metal ions among the octahedral and tetrahedral sites in the spinel structure of the nanoparticles and give detailed information on atomic distances. The samples consist of single-crystal nanoparticles with a composition corresponding to the Fe/Co ratio used in the synthesis. The degree of inversion is quite similar for all samples and close to the value found in a pure cobalt ferrite bulk sample

Exploring the Effect of Co Doping in Fine Maghemite Nanoparticles

We present a study of the structural, magnetic, and magneto-optical properties of a series of Co-substituted ferrite nanoparticles (NPs) prepared by thermal decomposition of metallo-organic precursors in high boiling solvents. The structural characterization, carried out by using several techniques (transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and magnetic circular dichroism measurements), showed all the samples are high crystalline, 5–6 nm spherical NPs with the cubic spinel structure typical of ferrites. The evolution of lattice parameters with cobalt content suggests that the material is Co-substituted maghemite, also confirmed by XAS and magneto optical (MO) characterizations. The investigation of the magnetic and magneto-optical properties displays peculiar trends with the cobalt content, the main features being the large increase of the saturation magnetization and the anomalous dependence of magnetic anisotropy which reaches its maximum values for intermediate compositions. The large tuneability of this material makes it possible to implement the performances of devices used in biomedical and sensing applications