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The influence of the surface modification on the magnetism of 4–14 nm sized core and core/shell gallium ferrites obtained by different preparation methods (Massart's and thermal decomposition from acetylacetonates) was studied. The physical properties of GaxFe3-xO4 were investigated in a wide range of Ga admixtures 0 ≤ x ≤ 1.5. Ga ions location at 8a or/and 16d positions of a spinel structure depends on the synthesis method and has a pronounced effect on the superparamagnetic properties of nanoparticles. Magnetization and Mössbauer experiments show the dominant superparamagnetic contribution for the nanoparticles with x > 0.8 with the blocking temperature TB significantly below 200 K. Surface-modified nanoferrites disclosed spontaneous magnetization that does not exceed 60 emu/g. [ABSTRACT FROM AUTHOR]

Mössbauer measurements on single crystal absorbers at room and at low temperatures were performed. The results are fully consistent with previously published reports by other groups. Spectra of single crystals were simultaneously analyzed including magnetic dipole and electric quadrupole interactions. The analysis shows that there is a small component of magnetic moments perpendicular to the magnetic easy axis. Mössbauer data seem not agree with commonly accepted ferrimagnetic structure of GaFeO3. [ABSTRACT FROM AUTHOR]

New data on gallium ferrite particles are reported. The results of studies of Fe3O4/GaxFe3 – xO4 and GaxFe3 – xO4/Fe3O4 (x = 0.2, 0.4, 0.6 and 0.8) nanoparticles by X-ray and neutron diffraction, small angle neutron scattering, transmission electron microscopy, magnetization measurements, and Mössbauer spectroscopy. The cubic core–shell ferrites structures were confirmed as single phases with a cell parameter of ∼8.388 Å independent of gallium content. The lack of preferences in occupancies of gallium sites was confirmed. The magnetic structure at room temperature, the stability of a disaggregated dispersion of nanoparticles in the temperature range 20–50°C, the radii of the cores, and the thickness of the coating layers, as well as the specific absorption of electromagnetic radiation rates were characterized. [ABSTRACT FROM AUTHOR]

We have succeeded in synthesizing orthorhombic Ga(1_X)Fe(1+X)03 (-0.05 ≤ x ≤ 0.5), hexagonal GayFe(2-y)O3 (0 ≤ y ≤1.8) and cubic Ga(1+Z)Fe(2-Z)04 (--0.1 ≤ z ≤ 0.8) nanograins of gallium ferrites using conventional precursors and an organic environment of Pechini scenario under atmosphericpressure conditions (SG method). Phase composition and homogeneity were analyzed using X-ray diffraction. Small angle neutron scattering disclosed ellipsoidal particle shapes of gallium iron oxides (GFO) crystallizing in orthorhombic (o-GFO) and hexagonal (h-GFO) symmetry and parallelepiped shapes of Ga(1+y)Fe(2-y)O4 (c-GFO) grains. Despite local agglomeration among the magnetic grains, the scanning electron microscopy and transmission electron microscopy images point to faced-elliptical shapes. The Mössbauer spectroscopy with magnetization measurements was carried out in the temperature range of 5-295 K. The analysis of gallium ferrites magnetism demonstrates that iron atoms locate with various probabilities in crystallography positions and the spontaneous magnetization preserves up to room temperature (RT). [ABSTRACT FROM AUTHOR]

Multicomponent single phase alloys were synthesized according to the idea of iron-average atom system. X-ray diffraction shows formation of bcc phase and traces of unidentified phase. Mössbauer spectra indicate presence of two components with different hyperfine magnetic field distributions. The high field component corresponds to the majority ferromagnetic phase. Few per cent of iron builds low field component. The dominant effect of annealing consists in an increase of the low field component. [ABSTRACT FROM AUTHOR]

In this study, the Mossbauer spectroscopy and the neutron powder diffraction were used for the characterisation of GaFeO3 samples prepared by two different methods, solid state reaction and sol-gel synthesis. The samples have similar structures that differ in distributions of Fe and Ga among the pertinent sites. The samples also differ in magnetic transition temperatures. We studied how to adopt the method of invariants, developed earlier for decomposition of the Mossbauer spectra into site components, to the case of magnetic interactions dominating over small quadrupole interactions. A combined neutron and Mossbauer data analysis has led to the determination of site assignment and the occupancies. [ABSTRACT FROM AUTHOR]

The so-called Bayesian reasoning is applied whenever uncertainty has to be considered as serious factor in interpretation of results. The paper presents analysis of the impact of inaccurate data on the straight line and quadratic relation fittings. This type of analysis is particularly important when one tries to decide on the type of dependence. The paper also shows examples of the Maximum Entropy Methods applied to the reconstruction of the hyperfine parameters distribution from the measured Mössbauer spectra of GaFeO3 and the electron-positron momentum distribution from the positron annihilation data of Gd. [ABSTRACT FROM AUTHOR]

A method for Mössbauer data treatment is proposed for texture-free samples, easily obtained as powdered absorbers. Although the results of the analysis do not contain full information about the parameters of hyperfine interactions, they are free of ambiguity typical for 3/2–1/2 nuclear-spin transitions because only experimentally available information is being considered. The method is particularly useful in cases where mixed interactions, e.g. magnetic dipole and electric quadrupole interactions are present. The method could be easily employed with the help of widely used standard Mössbauer packages when some constraints are applied. Advantages of the suggested procedure are illustrated on the example of interpretation of the Mössbauer spectra of UFe5Sn alloy characterized by many inequivalent sites of iron. [ABSTRACT FROM AUTHOR]

Mössbauer spectroscopic methods combined with the use of circularly polarized radiation offer element selective, unambiguous measurements of the orientation of hyperfine magnetic field at the nucleus. The paper presents applications of the method in investigations of antiferromagnets and distribution of magnetization inside iron-based nanoparticles. Selected examples showing development of Mössbauer conversion electron polarimetric methods are also reported. [ABSTRACT FROM AUTHOR]

Mössbauer polarimetry was used for investigations of orientations of Fe magnetic moments in a γ-Fe-Mn system. External magnetic field was applied to single crystal samples. Since the hyperfine field is a vector quantity, it forms a vector sum with the external magnetic field, and this quantity obviously depends on the magnetic structure of a system under study. Investigations with various orientations of external magnetic field with respect to the crystalline directions were performed. There is a clear experimental evidence that the distribution of Fe moments is present, which explains the already reported disagreement between simulated and measured results. Shapes of the spectra are best explained under the assumption of a coexistence of Q2 and Q3 structures. Influence of plastic deformation on the distribution of hyperfine fields is reported. [ABSTRACT FROM AUTHOR]

Mössbauer polarimetry is used for investigating the orientation of Fe magnetic moments in the nanocrystalline Fe0.48Al0.52 disordered alloy prepared by mechanical grinding. Local Fe magnetic moments and their contributions to the net magnetization at selected external fields and temperatures were estimated. It was found that the components of the Fe magnetic moments parallel to the net magnetizations reduce their values much faster with an increasing number of neighbouring Al atoms than the total iron moments. [ABSTRACT FROM AUTHOR]

Mössbauer measurements with circularly polarized radiation were performed on a nanocrystalline, disordered Fe48Al52 alloy. The analysis of the data for various polarization states resulted in the characterization of the hyperfine magnetic field distribution and the dependence of the average z-component of hyperfine field on the chemical environment. An increasing number of Al in the first coordination shell causes not only a decrease of magnetic moments but also introduces noncollinearity. [ABSTRACT FROM AUTHOR]

Properties of amorphous alloy Fe0.66Er0.19B0.15 are reported. A reorientation of the Fe and Er magnetic moments during sample cooling through the compensation point in a large magnetic field is found by means of monochromatic circularly polarised radiation. [ABSTRACT FROM AUTHOR]

The results of the Mössbauer effect measurements on bcc Cr rich Cr-Fe-Mn alloys in temperature range 12–296 K in zero- and in applied magnetic fields are reported. Monochromatic, circularly polarized radiation was used for investigation of iron moments alignment. Strong enhancement of internal hyperfine magnetic field induced by the applied magnetic field was detected and explained as due to dynamical effects. At high temperatures alignment of iron moments in antiferromagnetic phase is weakly magnetic field-dependent. At low temperatures the average hyperfine magnetic field is antiparallel to the net magnetization showing that iron moments are partly ordered by the applied field. [ABSTRACT FROM AUTHOR]

A reconstruction of the three dimensional distribution of the hyperfine magnetic field, isomer shift and texture parameter z from the Mössbauer spectra by the maximum entropy method is presented. The method was tested on the simulated spectrum consisting of two Gaussian hyperfine field distributions with different values of the texture parameters. It is shown that proper prior has to be chosen in order to arrive at the physically meaningful results. [ABSTRACT FROM AUTHOR]

The ferrite magnetic nanoparticles with core-shell structures were obtained in two step preparation process. The Mössbauer spectra obtained for particles of pure maghemite or magnetite and two layered core-shell one the magnetite on maghemite and maghemite on magnetite are very different from each other. The presented results show that interparticle and intraparticle interaction plays important role in overall magnetic properties as well. [ABSTRACT FROM AUTHOR]

A correction to the article "The Method of Invariants Applied to the Analysis of 57Fe Mössbauer Spectra" that was published in a previous issue is presented.