Mössbauer Investigation of γ-Fe₂O₃ Nanocrystals in Silica Matrix Prepared by the Sol-gel Method

Abstract

A series of Fe 2 O 3 -SiO 2 nanocomposites (25 weight % of Fe 2 O 3 ) has been prepared using a sol-gel method. Samples showing different features were obtained by varying the evaporation conditions acting on the surface / volume ratio of the starting sol. The samples were investigated using Mössbauer spectroscopy at low temperature. The Fe 2 O 3 nanoparticles have been identified as maghemite ( -Fe 2 O 3 ) particles. The samples show a superparamagnetic behavior with a blocking temperature that depends on the average particle size.

Iron(III) species dispersed in porous silica through sol–gel chemistry

“…The distribution of isomer shifts and quadrupole splittings results from the variety of local environments that the iron(III) ions experience in the amorphous xerogel. Both the average isomer shifts and quadrupole splittings are in complete agreement with those previously observed in iron(III) oxide doped aerogels and xerogels [40][41][42][43][44]. The appearance of broadened sextets below $30 K probably does not arise from ordered iron(III) oxides but rather from the onset, upon cooling, of slow paramagnetic relaxation [45,46] of the isolated iron(III) ions known to be present from UVvisible results and studies of magnetic properties, see below.…”

Low temperature superparamagnetic nanocomposites obtained by Fe(acac)3-SiO2-PVA hybrid xerogel thermolysis

“…Diverse approaches can be used in order to obtain desired properties of nanostructured materials [15][16][17][18][19], among which sol-gel method [20][21][22] could be a suitable one. Using the sol-gel route one can easily tailor and control the material morphology and texture [23].…”

Magnetic and in vitro heating properties of implants formed in situ from injectable formulations and containing superparamagnetic iron oxide nanoparticles (SPIONs) embedded in silica microparticles for magnetically induced local hyperthermia

“…The saturation magnetization of maghemite nanoparticles embedded in a silica matrix was indeed demonstrated to decrease drastically when the temperature increased from 77 to 300 K [49]. Although not clearly understood, this appears to be a consequence of the already-mentioned surface effects, prominent at the nanoscale, due to the paramagnetic external layer surrounding the ferrimagnetic core of the maghemite nanoparticles, resulting in a decreased magnetic diameter [50][51][52]. Because the magnetic moment is determined exclusively by the ferrimagnetic core where the spins are aligned as a result of the super-exchange interaction, the spontaneous magnetization consequently decreases [49].…”