A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe₂O₄(M = Mn, Co, Ni)

Abstract

The structural and magnetic properties of nanocrystalline manganese, cobalt, and nickel spinel ferrites dispersed in a highly porous SiO 2 aerogel matrix were studied. X-ray diffraction and high-resolution transmission electron microscopy indicate that single crystalline ferrite nanoparticles are well dispersed in the amorphous matrix. The cation distribution between the octahedral and tetrahedral sites of the spinel structure was investigated by X-ray absorption spectroscopy. The analysis of both the X-ray absorption near edge structure and the extended X-ray absorption fine structure indicates that the degree of inversion of the spinel structure increases in the series Mn, Co, and Ni spinel, in accordance with the values commonly found in the corresponding bulk spinels. In particular, fitting of the EXAFS data indicates that the degree of inversion in nanosized ferrites is 0.20 for MnFe 2 O 4 , 0.68 for CoFe 2 O 4 , and 1.00 for NiFe 2 O 4 . Magnetic characterization further supports these findings.

Cobalt Ferrite Nanoparticles Fabricated via Co-precipitation in Air: Overview of Size Control and Magnetic Properties

“…Fcc unit cells are stabilized by tetrahedral interstitial sites and octahedral interstitial sites, and, for the spinel structure, each fcc unit cell has twice as many available tetrahedral sites (sixty-four sites) as available octahedral sites (thirty-two sites) [25,31,[33][34]. In spite of this difference in available sites, owing to the fact that each fcc unit cell is made up of only fifty-six ions, specifically thirty-two oxygen anions, eight "A"…”

“…cations, and sixteen "B" cations, in which "A" and "B" refer to the general spinel structure (AB 2 O 4 ), clearly not all available interstitial sites are occupied in each fcc unit cell [25,31,34]. In fact twice as many octahedral sites as tetrahedral sites are actually occupied in each fcc unit cell [31,[34][35].…”

“…In fact twice as many octahedral sites as tetrahedral sites are actually occupied in each fcc unit cell [31,[34][35]. More precisely, in a normal spinel eight of the tetrahedral sites are occupied by "A" cations and sixteen of the octahedral sites are occupied by "B"…”

“…cations whereas in an inverse spinel structure only eight of the octahedral sites are occupied by "B" cations, eight other octahedral sites are occupied by "A" cations, and eight tetrahedral sites are occupied by the other half of the available "B" cations [25,31,[34][35]. as the way shown, to fill out the unit cell.…”

“…as the way shown, to fill out the unit cell. Recall that there are eight occupied tetrahedral sites and sixteen occupied octahedral sites [25,31,[34][35].…”