Jozef Sitek

Magnetic response of FeNbCuBSi RQ ribbons to bi-axial strain

Abstract Nanocrystalline strip samples of the FeNbCuBSi class that are macroscopically heterogeneous due to surface /volume differences have been investigated. This heterogeneity is found to be a general property of the class. It represents a base for mutual force influence between the surface and the majority volume beneath. The bi-axial in-plane stress exerted by the ribbon surfaces on the volume is demonstrated first of all by a magnetoelastic anisotropy. The contribution of the creep-induced anisotropy, which can build up under the surface stress at post-treatment temperature, is also found possible.

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.

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.

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.

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.

Surface Properties of a Nanocrystalline Fe–Ni–Nb–B Alloy After Neutron Irradiation

Abstract The effect of neutron radiation on the surface properties of the nanocrystalline (Fe0.25Ni0.75)81Nb7B12 alloy was studied. Firstly, amorphous (Fe0.25Ni0.75)81Nb7B12 ribbon was brought by controlled annealing to the nanocrystalline state. After annealing, the samples of the nanocrystalline ribbon were irradiated in a nuclear reactor with neutron fluences of 1×1016cm−2 and 1 × 1017cm−2 . By utilizing the magnetic force microscopy (MFM), topography and a magnetic domain structure were recorded at the surface of the ribbon-shaped samples before and after irradiation with neutrons. The results indicate that in terms of surface the nanocrystalline (Fe0.25Ni0.75)81Nb7B12 alloy is radiation-resistant up to a neutron fluence of 1 × 1017cm−2 . The changes in topography observed for both irradiated samples are discussed

Application Potential of Nanocrystalline Ribbons Still Pending

Application Potential of Nanocrystalline Ribbons Still Pending Nanocrystalline soft-magnetic ribbons promised a wide-spread practical use when introduced at the beginning of nineties. After 20 years of extensive research there are still unclear material problems which are thought to be the principal reason why these materials show but marginal use. Poorly controllable magnetic anisotropy due to spontaneous intrinsic macroscopic stress that comes from an inevitable heterogeneity of the ribbon materials is pointed to in this work. Certain stress-based mechanisms are shown to induce the unintended anisotropy in the already familiar Finemets as well as in the newer Hitperms. Hysteresis loops, domain structure and power loss is used to reveal the anisotropy consequences and particular connected but still unanswered questions are pinpointed.

Influence of External Factors on Amorphous and Nanocrystalline Soft Magnetic Alloys Studied by Mössbauer Spectroscopy

In this paper, a review of recent 57Fe Mössbauer spectroscopy (MS) studies of external influence on the properties of amorphous and nanocrystalline Fe- and Co-based alloys is submitted. Different types of alloys (FeCuNbZr, FeCuNbSiB, FeCoCuNbB, CoFeZrB and CoFeSiB) in the form of original amorphous and nanocrystalline ribbons were subjected to different external factors: different annealing atmospheres, mechanical stress (for example influence of ball-milling) and tensile stress. It will be shown that the Mössbauer spectrometry is a suitable tool for such studies because the measured spectral parameters are very sensitive to the changes in the vicinity of the probe 57Fe-nuclei and thus, this technique provides a wide variety of information about structural and magnetic behavior of Fe-containing materials.

Nanocrystalline alloys of Fe-Cu-Nb-Si-B after neutron irradiation

Transmission Mössbauer spectroscopy was used to study changes induced by irradiation of amorphous and nanocrystalline samples. In an as-cast sample neutrons mostly affect the orientation of a net magnetic moment. The average hyperfine field decreases towards higher neutron fluencies. In the case of the nanocrystalline samples a new disordered structure is created in the amorpous remainder corresponding to boride phases as it is shown in the samples isothermally heated from 1 to 8 hours. The structural changes of the amorphous remainder depend on the stage of crystallization and total neutron fluencies.