F.A. Tourinho

Use of Raman micro-spectroscopy in the characterization of MIIFe2O4 (M = Fe, Zn) electric double layer ferrofluids

MIIFe2O4 (M = Fe, Zn) electric double layer ferrofluids (edl-ferrofluids) were investigated and characterized by Raman micro-spectroscopy as solids (powder) or in solution forming magnetic fluids. The Raman spectra showed that the nanoparticles forming the magnetic fluids have different compositions depending on the MII ion used in their preparation. In the case of FeFe2O4 edl-ferrofluid, maghemite, magnetite, an amorphous non-stoichiometric oxyhydroxide [FeOx(OH)3 − 2x, x<1] and Fe(OH)3 phases are present. In the case of the ZnFe2O4 edl-ferrofluid, a magnetite-like structure where the FeII centers were replaced by the ZnII ions is present. A model of the distribution of the different chemical phases on the nanoparticles is presented. The Raman spectrum of the FeFe2O4 edl-ferrofluid excited close to an absorption band of the sample at 650 nm presents several Raman features above 900 cm−1 that are not observed for the ZnFe2O4 edl-ferrofluid sample. These results have been interpreted considering the resonant excitation of the density of phonon states with k ≠ 0 due to quantum size effects. Copyright

Biocompatible magnetic fluid precursors based on aspartic and glutamic acid modified maghemite nanostructures

Abstract Biocompatible magnetic fluid precursors based on chemically modified maghemite nanostructures (γ-Fe 2 O 3 ) are able to chemisorb aspartic and glutamic acids, as shown by conductometric measurements. The amino acids adsorb onto the maghemite surface following an adsorption isotherm. The modified nanoparticles formed a stable colloidal solution at a pH of 5–8. Raman and FTIR spectroscopy directly showed that the investigated amino acids adsorb on the maghemite surface in the form of their respective salts, glutamate and aspartate.

Biological effects of magnetic fluids: toxicity studies

Toxicity of ionic and citrate-based magnetic fluids administrated intraperitoneally to mice was investigated through cytogenetic analysis, evaluation of mitotic index and morphological and cytometric alterations. Both magnetic fluid samples cause severe inflammatory reactions, being very toxic and thus not biocompatible. Peritoneal cells and tissues studies may provide a useful strategy to investigate the in vivo biological effects of magnetic nanoparticles.

Magnetic and optical properties of ionic ferrofluids based on nickel ferrite nanoparticles

New ionic ferrofluids containing NiFe2O4 nanoparticles of size ⩽10 nm are investigated. The crystalline structure of the particles is probed by transmission electron microscopy and x-ray scattering. Static magnetization and field-induced birefringence measurements are performed on three samples differing by particle volume fraction. Cross analyzing of the results of those two types of macroscopic tests completely rejects a simple single-domain particle model but readily supports the two-component scheme of a particle as consisting of a core with a uniform magnetization and a surface layer of comparable thickness stowed with a spin-glass-like arrangement.

Toxic effects of ionic magnetic fluids in mice

Abstract Toxicity of ionic and tartrate-based magnetic fluids administered intraperitoneally to mice was investigated through morphological and cytometric alterations and cytogenetic analysis. Both magnetic fluids cause cellular death, mutagenicity and severe inflammatory reactions, being very toxic and thus not biocompatible. Peritoneal cell and tissue studies may provide a useful strategy to investigate the in vivo biological effects of magnetic nanoparticles.

NiFe2O4 nanoparticles in ferrofluids: evidence of spin disorder in the surface layer

We show that surface magnetic properties of NiFe2O4 nanoparticles constituting ionic ferrofluids can be investigated in macroscopic experiments. Cross-analysis of static magnetization and field-induced birefringence prove that the particles consist of a uniformly magnetized core and a spin-disordered surface layer of comparable thickness. r 2002 Elsevier Science B.V. All rights reserved.

Electron paramagnetic resonance study of ionic water-based manganese ferrite ferrofluids

Abstract We report for the first time electron paramagnetic resonance linewidth measurements in an ionic water-based ferrofluid. The linewidth broadening is studied as a function of the particle-particle distance. We change the average particle-particle distance from 20 to 89 nm by diluting a concentrated sample with water. Magnetic and electric interactions between adjacent particles are used to explain the experimental data.

Surface spin freezing of ferrite nanoparticles evidenced by magnetization measurements

Magnetization and in-field Mossbauer measurements were performed on copper ferrite nanoparticles with average sizes ranging from 3.5 to 10.4nm. Our results show that the nanoparticles are well-crystallized single domains with a magnetically disordered surface shell. A sharp increase in the saturation magnetization at low temperatures, in addition to the usual modified Bloch behavior, was observed for the smallest particles. This jump in magnetization curves seems to be related to the freezing of the surface spins below a temperature of about 45K.

Optical properties of nickel ferrite ferrofluids

We investigate magneto-optical properties of chemically synthesized ionic ferrofluids based on nickel ferrite nanoparticles. These new ferrofluids with potential biological applications become birefringent under low magnetic fields. Both a static and a dynamic probing are here presented.

Low temperature experimental investigation of finite-size and surface effects in CuFe 2 O 4 nanoparticles of ferrofluids

Abstract Size sorted magnetic nanoparticles based on copper ferrite have been chemically synthesized. Their magnetic properties have been investigated at low temperature using Mossbauer spectroscopy and magnetisation measurements. The thermal variation of the magnetization is strongly affected by finite size and surface effects. Indeed, the Mossbauer results show that the structure of the nanoparticles is made of a monodomain ordered core and a surface shell of disordered spins. Introduction Magnetic ferrite nanoparticles have been studied for the last decades from both scientific and technological point of view [1]. They are largely used as components in recording tape, flexible disc recording media, magnetic fluids as well as biomedical material. These applications require the knowledge of the properties of nanostructured systems and how bulk properties are modified as the crystal size decreases to the nanometric range [2]. As an example, in γ-Fe 2