Evolution of the Structure and Magnetic Properties of FeCo Nanoparticles in an Alumina Aerogel Matrix

Abstract

Nanocrystalline gamma-Al2O3 and FeCo-Al2O3 nanocomposite aerogels with high surface areas and pore volumes were prepared by high-temperature supercritical drying of alcogels obtained by a fast sol-gel procedure. The formation of gamma-Al2O3 occurs via a sequence of stages: in the parent aerogel an alkyl derivative of boehmite is observed whose calcination gives rise to a disordered phase and finally to gamma-Al2O3 which is stable up to 1000 degreesC. In the presence of iron and cobalt, calcination of the aerogel gives rise to a spinel phase similar to gamma-Al2O3 where metal ions partially fill the vacancies. Nanocomposites constituted of FeCo alloy nanoparticles dispersed into gamma-Al2O3 matrix are obtained via reduction in hydrogen flow of the aerogels containing iron and cobalt. The amount and average size of the nanoparticles depends both on the temperature and time of the reduction treatment and affects the resulting magnetic properties. All the reduced aerogels show superparamagnetic behavior, but the collective magnetic properties are strongly dependent on the amount and mean size of the alloy nanoparticles

Epoxide-assisted alumina aerogels by rapid supercritical extraction

“…These peaks agree well with the characteristic XRD pattern for gelatinous boehmite or pseudoboehmite. 3,28,32 Pseudoboehmite is a poorly crystallized form of boehmite due to excess water contained in the structure (AlOOH•1.7H 2 O). 3,28,32,33 The peak at 2θ = 9° is the characteristic XRD peak of an alkoxyalumoxane prepared using ethanol.…”

“…3,28,32 Pseudoboehmite is a poorly crystallized form of boehmite due to excess water contained in the structure (AlOOH•1.7H 2 O). 3,28,32,33 The peak at 2θ = 9° is the characteristic XRD peak of an alkoxyalumoxane prepared using ethanol. 31,32 Alkoxyalumoxane materials have XRD patterns which are similar to pseudoboehmite, but with larger interlayer spacings due to the presence of alkyl groups between the layers of the structure.…”

Single-crystalline FeCo nanoparticle-filled carbon nanotubes: synthesis, structural characterization and magnetic properties

“…Different techniques have been applied for the synthesis of these magnetic nanoparticles (MNPs), such as mechanical alloying [23], electrodeposition [24], radio frequency (rf)-plasma torch [25], sol–gel methods [26–27], reverse micelle systems [28] and thermal decomposition of bimetallic alloys [29]. However, many of these techniques are relatively expensive (either high-cost starting materials or high-energy consumption), and involve difficulties in controlling the size and morphology of the nanoparticles.…”

Superparamagnetic Composites: Magnetism with No Memory

“…[113] Alumina matrixes have also been used for dispersion of SPNPs. [114] The problem with alumina is that it also suffers from dissolution at basic pH. Zeolite matrixes have also been used for the stabilization of ultrasmall Co nanoparticles; however, while this is interesting from a fundamental side, the magnetic moment is too low for practical applications.…”