Mössbauer investigation of non-aggregated γ-Fe2O3 particles

Investigation by Mössbauer spectroscopy of non-aggregated nanometric -Fe₂O₃ particles dispersed in polymer is reported. Magnetic interactions between the particles were controlled by varying the particle concentration in the polymer. The results show that over the investigated range, the interactions make the relaxation time shorter. Infield experiments show spin canting which increases with decreasing particle size.     

Biodegradation of magnetic nanoparticles evaluated from Mössbauer and magnetization measurements

In order to extract a quantitative information about characteristics of the magnetic nanoparticles injected into a living organism it is necessary to define a model of the magnetic dynamics for fitting self-consistently the whole set of the experimental data, specifically, the evolution of Mössbauer spectral shape with temperature and external magnetic field as well as the magnetization curves. We have developed such a model and performed such an analysis of the temperature- and magnetic field-dependent spectra and magnetization curves of nanoparticles injected into mice. This allowed us to reliably evaluate changes in the characteristics of the residual particles and their chemical transformation to paramagnetic ferritin-like forms in different mouse organs as a function of time. Actually, the approach makes it possible to quantitatively characterize biodegradation and biotransformation of magnetic nanoparticles delivered in a body.     

Magnetic properties of γ-Fe2O3 nanoparticles encapsulated in surface-treated polymer spheres

Mössbauer and magnetic characterization of polymer-dispersed γ-Fe₂O₃ nanoparticles treated under different chemical processes are reported in this work. X-ray powder diffraction analysis provides a mean particle size of D ~ 8.0 nm. Whereas Mössbauer spectroscopy data suggest the presence of only Fe^3?+? ions, magnetization measurements indicate the occurrence of a freezing phenomenon in agreement with the thermal evolution of Mössbauer spectra. A core–shell model was used to determine a magnetically disordered layer (shell) of d ~ 1.0 nm covering a region of collinear magnetic moments (core). The chemical treatments with H₂O₂ and Na₂S₂O₈ modify notoriously the magnetic response of the polymer-dispersed nanoparticles.     

Mössbauer spectroscopy studies of the magnetic properties of ferrite nanoparticles

Studies of the ferrite nanoparticles prepared by the chemical decomposition of iron chlorides with a various ratio ξ = Fe³⁺/Fe²⁺ are herein presented. The microstructure and the magnetic properties have been studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The TEM studies show that the nanoparticles have almost a spherical shape with the diameter of (12 ± 2) nm for all samples. The measured XRD pattern was mainly composed of lines which were indexed with a cubic spinel structure. The analysis of the Mössbauer data shows that the microstructure of the nanoparticles consists of the core formed by nonstoichiometric magnetite and maghemite shell. A small amount of hematite, probably on the surface of the nanoparticles with ξ = 1.75, 2.0, was detected. At temperatures T ≤ 150 K the spin canting of surface maghemite with ξ = 2.25 was observed while for the samples with ξ = 1.75, 2.0 such effect was suppressed by the presence of hematite on the surface of the nanoparticles. Infield Mössbauer spectra with ξ = 1.75, 2.0 show that magnetic moments of the magnetite/maghemite core are parallel while magnetic moments of the surface hematite are perpendicular to the direction of the external magnetic field.     

Mössbauer spectroscopy,X-ray diffraction and magnetic measurements of iron-nickel ultrafine particles

Iron-nickel ultrafine particles with a composition in the Invar region (38–50% Ni) were prepared by the gas-evaporation-coalescence technique. The chemical composition was checked by electronprobe microanalysis, while X-ray diffraction Rietveld refinement was used to characterize the structure as well as to estimate the particle size. The temperature and field dependence of the magnetizationM(B, T) was measured for 0B25 kOe in the temperature range 4.2 KT400 K. Transmission Mössbauer spectra were taken at room temperature and at liquid helium temperature. The results obtained show that the predominant phase is a disordered Ni-rich alloy.On leave from Physics Department, University of Khartoum, P.O. Box 321, Khartoum, Sudan.     

57Fe Mössbauer spectra study of coated α-Fe2O3 nanoparticles

Nano-sized -Fe₂O₃ particles coated with polar organic molecules have been studied using the Mössbauer spectroscopy method. The -Fe₂O₃ nanoparticles were prepared by the microemulsion method. The average particle size of the Fe₂O₃ particles is about 24 Å. Because the particle size is so small that the Mössbauer spectra of the -Fe₂O₃ samples only consist of a quadrupole-split central line. It was proved that the Isomer Shifts (DIS) and the Quadrupole Splitting (DQS) changed as the refluxing time prolongs and the refluxing temperature increases during the preparation of the Fe₂O₃ nanoparticles, which implied an enhancement of the surface electrofield gradient formed by the surface coated polar molecules during the refluxing process.     

Magnetite nanoparticles as-prepared and dispersed in Copaiba oil: study using magnetic measurements and Mössbauer spectroscopy

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization and Mössbauer hyperfine parameters which were related to the interactions of Copaiba oil polar molecules with iron cations on magnetite nanoparticle’s surface.     

Mössbauer spectroscopy and magnetic studies of orientated textured Fe3O4 ferrofluid

Nano scale magnetite based ferrofluid is synthesized by chemical co pre cipitation technique and stabilized with oleic acid. Magnetization and viscosity measurements were used to optimize for texturing purpose. The freeze-textured ferrofluid in two configurations, namely, (1) field texture system (FTS) and (2) zero field texture system (ZTS) are investigated by magnetization measurements at 298 K and Mössbauer spectroscopy measurements at 77 and 298 K. These results are analysed on the basis of the contributions from collective superparamagnetic reversal and the strength of the inter particle interactions.     

Hydrogenation of FeCoZr–Al2O3 nanocomposites studied by Mössbauer spectroscopy and magnetometry

Hydrogenation effects on crystalline and magnetic structure of nanocomposites (FeCoZr) _x (Al₂O₃)_100???x , 38?≤?x?≤?63 at.% are studied by ⁵⁷Fe Mössbauer spectroscopy and magnetometry. Variations of local structure, blocking temperature and mean FeCoZr nanoparticles’ volume are discussed with respect to (i) composition and (ii) two competing processes—H₂ incorporation and annealing—occurred during treatment in H₂ plasma.     

Structural, static and dynamic magnetic properties of dextran coated γ-Fe(2)O(3) nanoparticles studied by (57)Fe NMR, M?ssbauer, TEM and magnetization measurements

The structural and magnetic properties and spin dynamics of dextran coated and uncoated γ-Fe(2)O(3) (maghemite) nanoparticles have been investigated using high resolution transmission electron microscopy (HRTEM), (57)Fe nuclear magnetic resonance (NMR), M?ssbauer spectroscopy and dc magnetization measurements. The HRTEM observations indicated a well-crystallized system of ellipsoid-shaped nanoparticles, with an average size of 10 nm. The combined M?ssbauer and magnetic study suggested the existence of significant interparticle interactions not only in the uncoated but also in the dextran coated nanoparticle assemblies. The zero-field NMR spectra of the nanoparticles at low temperatures are very similar to those of the bulk material, indicating the same hyperfine field values at saturation in accord with the performed M?ssbauer measurements. The T(2) NMR spin-spin relaxation time of the nanoparticles has also been measured as a function of temperature and found to be two orders of magnitude shorter than that of the bulk material. It is shown that the thermal fluctuations in the longitudinal magnetization of the nanoparticles in the low temperature limit may account for the shortening and the temperature dependence of the T(2) relaxation time. Thus, the low temperature NMR results are in accord with the mechanism of collective magnetic excitations, due to the precession of the magnetization around the easy direction of the magnetization at an energy minimum, a mechanism originally proposed to interpret M?ssbauer experiments in magnetic nanoparticles. The effect of the surface spins on the NMR relaxation mechanisms is also discussed.     

X-ray diffraction and Mössbauer spectroscopy of high energy ball-milled α-Fe2O3/TiO2 composite powders

α–Fe₂O₃/TiO₂ Composite powders have been prepared by high energy ball-milling for different times. The composites were studied using Mössbauer Spectroscopy (MS) and X-ray diffraction (XRD). The patterns of XRD show broadening in the diffraction peaks, indicating a decrease in the particle size of the composites with milling time. Also, the XRD patterns show an evolving new structural phase correlated with an evolving Titanium ferrite species with milling time. Mössbauer Spectroscopy shows the evolving titanium ferrite species characterized by a quadrupole doublet at the expense of the α–Fe₂O₃ represented by the magnetic sextet. The doublet corresponding to the Ti-ferrite phase dominates the Mössbauer spectra at long milling time (greater than 100 h of milling).     

Mössbauer Study of the Magnetic Transition in ϵ-Fe2O3 Nanoparticles Using Synchrotron and Radionuclide Sources

JETP Letters - Nuclear γ-resonance experiments with energy and time resolved detection are carried out with ϵ-F2O3 nanoparticles and a 57Co(Rh) laboratory Mössbauer source of γ...     

Magnetic properties of Yb Mo O and Gd Mo O from rare earth Mössbauer measurements

Using ¹⁷⁰Yb and ¹⁵⁵Gd M?ssbauer measurements down to ∼ 0.03 K, we have examined the semiconducting pyrochlore Yb₂Mo₂O₇ where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd₂Mo₂O₇ where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and ¹⁷²Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb₂Mo₂O₇ and modest in Gd₂Mo₂O₇. Magnetic irreversibilities occur at 17 K in Yb₂Mo₂O₇ and at 75 K in Gd₂Mo₂O₇ and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd₂Mo₂O₇, we observe the steady state Gd hyperfine populations at 0.027 K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic. Received 13 January 2003 Published online 4 June 2003 RID="a" ID="a"e-mail: hodges@drecam.saclay.cea.fr     

Characterization of magnetic nano-fluids via Mössbauer spectroscopy

The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mössbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mössbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.     

Nickel-induced magnetic behaviour of nano-structured α-Fe2O3, synthesised by facile wet chemical route

We report the synthesis of pristine and nickel containing iron oxide (α-Fe₂O₃) nanocrystallites by facile environmentally benign wet chemical process. The magnetic behaviour of the samples has been found to change progressively with nickel content. The Mössbauer spectra revealed the precipitation of secondary phase of nickel ferrite (NiFe₂O₄) at ～2?wt% nickel contents. The transmission electron micrographs together with asymmetric magnetic hysteresis loop have confirmed the formation of core–shell structure. The Morin temperature of nanostructured α-Fe₂O₃ as estimated by superconducting quantum interference device has been found to be 257, 245, 247 and 242?K at nickel content of 0, 1, 2 and 4?wt%, respectively. The similar trends of increase/decrease in Morin temperature have been noticed by Mössbauer analysis. Furthermore, below Morin temperature, the temperature range of coexisted antiferromagnetic and ferromagnetic states has been found to increase with increase in nickel content.