Maghemite–silica nanocomposites: sol–gel processing enhancement of the magneto-optical response

Abstract

The preparation and processing of maghemite-silica gel nanocomposites have been investigated in order to maximize their magneto-optical response for magnetic field sensing applications. In situ precipitation of maghemite nanoparticles from an iron salt precursor during the sol-gel processing of the silica matrix has been carried out while controlling the time, temperature, and environment at each step of the whole process. In this paper, the nanostructural, magnetic, and magneto-optical properties of these materials are correlated with the processing path followed, from the starting sol to the partially densified monolith. Results demonstrate that introducing a washing treatment prevents the formation of hematite phase as well as an excessive particle agglomeration. Different processing conditions of identical sols may lead to nanocomposites with a Verdet constant at low magnetic fields (0.01 T) ranging from 200 to 950 rad T(-1) m(-1), which is the typical value of commercial terbium gallium garnets used in Faraday rotators.

One-step room temperature synthesis of very small γ-Fe2O3 nanoparticles

“…Diverse routes for synthesizing g-Fe 2 O 3 NPs are reported: solgel synthesis [4], electron beam deposition [5], mechanochemical synthesis [6] and pyrolysis [7], among others. However, the conventional method to obtain g-Fe 2 O 3 NPs is the oxidation of magnetite [8,9] in where particles size exceeds 12 nm.…”

Highly crystalline superparamagnetic iron oxide nanoparticles (SPION) in a silica matrix

“…Complex magnetic properties of nanosized iron oxides have been widely discussed and a wide range of magnetic properties has been obtained [1,[56][57][58][59][60][61][62]. Dutta et al reported nearly defect-free maghemite nanocrystals of a size of about 7 nm, high saturation magnetization M S = 80 emu/g close to bulk value, whereas at the same time, very low coercivity H C = 20 Oe was obtained [63].…”

“…Among them the sol-gel method has been shown to be very useful for preparation of iron oxide nanoparticles dispersed in an amorphous silica matrix. Silica is convenient because of its nontoxic nature, high biocompatibility, prevention of agglomeration, temperature resistance, chemical inertness and adjustable pore diameter [1,2,8,10,21,32,36,37,49,50,[52][53][54]57,61,67,[81][82][83][84].…”

Synthesis and Characterization of Magnetic γ-Fe₂O₃/Al₂O₃ Core-Shell Nanocomposites

“…For example, it has already been extensively used as a magnetic recording material for a long time [3]. Besides, it is also widely used in drug delivery, catalysis, magneto-optical device, ferro-fluids, and magnetic refrigeration [4][5][6][7][8]. Although MNPs have already been studied for many years, research on their potential use in stealth aircrafts as electromagnetic and microwave absorbing material is now the hot topic in military application [9,10].…”