Július Dekan

Influence of Structure Evolution on Magnetic Properties of Fe–Ni–Nb–B System

The effect of combined presence of iron and nickel has been studied in rapidly quenched amorphous (Fe-Ni) 81Nb7B12 system with the ratio of Fe/Ni=2/1 and 1/2 in as-quenched state and after annealing. Field dependencies of magnetostriction as well as the values of saturation magnetostriction were correlated with the evolution of nanocrystalline structure in amorphous matrix in the temperature range from ~ 700 to 800 K and after complete crystallization above 900 K. Intervals of stability and transformation regions were determined from temperature dependencies of electrical resistivity. The structure after annealing at selected temperatures was identified by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction. MO¿ssbauer spectroscopy was used only as a complementary method to demonstrate the behaviour and development of the paramagnetic (FeNi) 23B6 phase from the original as-quenched structure. MO¿ssbauer and magnetostriction measurements were performed at room temperature. The observed field dependencies of magnetostriction are a combination of magnetostrictions of ferromagnetic and paramagnetic phases formed during the transformation process, namely, the nanocrystalline cubic Fe-Ni phases and face-centered cubic (fcc)-type structure (FeNi)23B6, as identified from the structure analyses. The transition from purely ferromagnetic to partially paramagnetic state is well observed in the evolution of MO¿ssbauer spectra evolution. Different ratios of both ferromagnetic components Fe and Ni lead to a change of the structure of the nanocrystalline phases and thus also to a change in the magnetic behavior of the system.

Iron in spleen tissues

This contribution aims in characterization of structural positions of iron in human and horse spleen. 57Fe Mossbauer spectroscopy was employed as a principal method of investigation in addition to X-ray diffraction and transmission electron microscopy (TEM). At room temperature, ferritin nanoparticles exhibit superparamagnetic behavior due to their small dimensions. Corresponding Mossbauer spectra show doublet-like patterns. Experiments performed at low temperatures unveiled presence of magnetically split components and enabled to determine the blocking temperature. Dimensions of Fe-containing species were established from detailed analyses of TEM images.

Magnetic and Surface Properties of High-Induction Nanocrystalline Fe-Nb-Cu-B/P-Si Ribbons

High-induction Si-poor Fe-Nb-Cu-B-Si Finemet ribbons annealed in inert gas ambience are known to build oxides and prefer surface crystallization. Phosphorus-3 at% of P instead of B was substituted to see how it can influence these surface effects. The off-axis magnetic anisotropy caused by surfaces squeezing the ribbon interior was reduced and it was found out that the major source of the squeeze is the surface crystallization and not the oxides. Phosphorus appears to hamper preferentially the surface crystallization. The substitution also improves the magnetic softness of vacuum-annealed ribbons by grain size reduction. Slight reduction of saturation induction is a minor sacrifice to the improvements.

On the validity of the fitting model of transmission Mössbauer spectra of Fe78Si9B13 amorphous alloy

57Fe Mossbauer spectrometry in transmission geometry is used to study the effect of the wheel’s tangential velocity in a melt spinning method on the resulting properties of Fe78Si9B13 amorphous ribbons. According to the spectra obtained at room temperature all samples are ferromagnetic and no signs of crystalline phases were observed. The acquired Mossbauer spectra were fitted by two different models employing distributions of hyperfine magnetic fields, P(B). The fitting models differ in the ranges of hyperfine magnetic fields, B, which were taken into consideration when P(B) distributions were constructed. We have used the NORMOS fitting program. At the first glance it is quite feasible to fit spectra using both models. They are compared in terms of the shapes of P(B) distributions, their average values , standard deviations, chi-squares and other spectral parameters. Majority of the considered parameters do not considerably differ for both models within the experimental error range. One exception is ...

Properties of nanocrystalline alloys after electron beam irradiation of amorphous precursor

Electron-beam was used for irradiation of amorphous precursors of (Fe64Co21B15)95P4Cu1 and (Fe64Co21B15)96P4 alloys and then by heat treatment nanocrystalline structure was created. Changes in microstructure were not observed under the doses of 4 MGy. All irradiated samples were compared with non-irradiated one. Samples were studied by Mossbauer spectroscopy and XRD. Irradiation had an influence on the volumetric fraction of the constituent phases and on their magnetic microstructure. After the heat treatment nanocrystalline sample prepared from irradiated precursor contained more crystalline phase than non-irradiated. This technology of prepare of nanocrystalline alloys indicates that irradiation of amorphous precursor has an influence on the final structure and properties of nanocrystalline alloy.Electron-beam was used for irradiation of amorphous precursors of (Fe64Co21B15)95P4Cu1 and (Fe64Co21B15)96P4 alloys and then by heat treatment nanocrystalline structure was created. Changes in microstructure were not observed under the doses of 4 MGy. All irradiated samples were compared with non-irradiated one. Samples were studied by Mossbauer spectroscopy and XRD. Irradiation had an influence on the volumetric fraction of the constituent phases and on their magnetic microstructure. After the heat treatment nanocrystalline sample prepared from irradiated precursor contained more crystalline phase than non-irradiated. This technology of prepare of nanocrystalline alloys indicates that irradiation of amorphous precursor has an influence on the final structure and properties of nanocrystalline alloy.

Mössbauer spectrometry analysis of Fe 78 Si 9 B 13 metallic glass prepared with different quenching wheel speed

Impact of the wheel speed upon microstructure and hyperfine interactions of amorphous Fe78Si9B13 ribbons was studied. Mössbauer spectrometry, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and magnetic measurements were applied. Though minor effects of wheel speed upon macroscopic magnetic properties was found, notable changes in repositioning of magnetic moments of the resonant atoms caused by modifications in the topological short-range order (SRO) were unveiled. No deviations were observed in the chemical SRO. The observed effects were enhanced after annealing at moderate temperatures.

Change of magnetic properties of nanocrystalline alloys under influence of external factors

Nanocrystalline (Fe3Ni1)81Nb7B12 alloys were irradiated using different types of radiation and subsequently studied by Mossbauer spectroscopy. External magnetic field of 0.5 T, electron-beam irradiation up to 4 MGy, neutron irradiation up to 1017 neutrons/cm2 and irradiation with Cu ions were applied on the samples. All types of external factors had an influence on the magnetic microstructure manifested as a change in the direction of the net magnetic moment, intensity of the internal magnetic field and volumetric fraction of the constituent phases. The direction of the net magnetic moment was the most sensitive parameter. Changes of the microscopic magnetic parameters were compared after different external influence and results of nanocrystalline samples were compared with their amorphous precursors.

Investigation of corrosion-resistant LC200N steel by back scattering Mössbauer spectrometry

In this work we focus on characterization of LC200N steel by back-scattering Mossbauer spectrometry (MS). This geometry was used due to high sample thickness (0.5 mm). MS is a method suitable for determination of iron compounds and their properties in steels. We investigated samples with three different thermal treatments: non-hardened, hardened, and hardened with subsequent rapid quenching. Disk-shaped samples were cut off from original rods and polished from one side. The effect of surface treatment was investigated, too. Variations in microstructure imposed by different thermal and surface treatments were unveiled by Mossbauer parameters of backscattering spectra taken from both sides of the investigated samples. In this way, differences between the original as-cut and polished surfaces of the disks were unveiled.

Analysis of Košice Meteorite by Mössbauer Spectroscopy

Abstract The 57Fe Mössbauer spectroscopy method was used to investigate iron-containing compounds in town Košice meteorite fallen on the territory of Slovakia in February 2010. The results showed that the Mössbauer spectra consisted of magnetic and non-magnetic components related to different iron-bearing phases. The non-magnetic phase includes olivine, pyroxene and traces of Fe3+ phase and the magnetic component comprises troilite (FeS) and iron-rich Fe-Ni alloy with hyperfine magnetic field typical for kamacite. Samples from meteorite were obtained in powder from different depths to inspect its heterogeneous composition. The content of kamacite increases to the detriment of troilite from the surface toward the centre of the sample. Measurements at liquid nitrogen temperature confirmed phase composition of investigated meteorite. Main constituent elements of studied samples were also determined by X-ray fluorescence analysis.

Influence of Quenching Rate on the Structure, Morphology, and Hyperfine Parameters of Amorphous Ribbons

Abstract In this work, an amorphous alloy with the nominal composition of Fe78Si9B13 was produced by a melt spinning method. Using different velocities of a quenching cooper wheel enabled us to study the influence of quenching rate upon the structural characteristics of the resulting ribbons. Structural features of the samples were checked by Mössbauer spectroscopy and X-ray diffraction. The latter performed in a grazing angle geometry enabled us to explore both sides of the as-quenched ribbons. The onset of crystallization was estimated by differential scanning calorimetry (DSC) measurements. Surface features of the ribbons were examined by Scanning Electron Microscopy (SEM). In order to observe structural relaxation phenomena the samples were annealed below the onset of crystallization at 450 °C for 1 hour in Ar protective atmosphere. Even though the annealed ribbons are still amorphous relevant changes were observed in their hyperfin parameters as derived from Mssbauer spectrometry.