Surface magnetostriction of FeCoB amorphous ribbons analyzed using magneto-optical Kerr microscopy

Surface sensitive magneto-optical Kerr microscopy completed with the special self-made sample holder is used for studying the magneto-elastic behaviour in the surface of the as-quenched amorphous Fe73Co12B15 alloy. The 10, 5, and 3 mm wide and approximately 34 mu m thick ribbons were prepared by the conventional planar flow casting process. The experimental setup allows for a simultaneous application of an external magnetic field in the directions parallel and perpendicular to the ribbon axis and of compression stress from one side of the sample, resulting in tensile stress in opposite side. The distributions of tensile stresses in the measured surface were modelled by the finite element method. The observed changes of the magnetic domains and hysteresis loop anisotropy field under applied stress are evaluated using the Becker-Kersten method. This resulted in the determination of the local surface magnetostrictive coefficient from an area of about 200 mu m in diameter. The obtained values ranged between 37-60 ppm and were well comparable with the bulk value presented in the literature.Web of Science132art. no. 25

Microstructural analysis and magnetic characterization of native and magnetically modified montmorillonite and vermiculite

Two clay minerals of the similar 2 : 1 layer structure and chemical composition, vermiculite and montmorillonite, were studied using a wide spectrum of experimental methods in their original states and the magnetically modified states after mixing with microwave-synthesized iron oxide particles. This magnetic modification led to different microstructural morphology influencing magnetic behaviour at room and more pronounced at low temperatures.Web of Scienceart. no. 373810

Effect of iron impurities on magnetic properties of nanosized CeO2 and Ce-based compounds

CeO2 samples prepared by three technological procedures from the same cerium source, namely cerium (III) nitrate hexahydrate, are studied from the viewpoint of structure, chemical and phase composition, and micro- and macro-magnetic properties. The scanning and transmission electron microscopies completed by energy-dispersive X-ray (EDX) analysis yield nano-structural natures and homogenous chemical compositions of the ceria samples, confirmed also by X-ray diffraction. The diamagnetic, paramagnetic, and ferromagnetic phases in all samples follow from an analysis of the room- and low-temperature measurements of hysteresis loops. Iron impurities in ppm amounts are clearly detected by Fe-57 Mossbauer spectrometry not only in the ceria samples but also in the selected input chemicals used for their preparation. This contributes to the explanation of the magnetic behaviour of nanosized ceria.Web of Science92art. no. 22

Influence of preparation technology on microstructural and magnetic properties of Fe2MnSi and Fe2MnAl Heusler alloys

Microstructural and magnetic properties of the X(2)YZ, namely Fe2MnSi and Fe2MnAl, Heusler alloys have been studied from the viewpoint of technology for their production and for the Z element effect. First, arc melting was applied to produce button-type ingots from which samples in a form of 500 mu m thick discs were cut. Second, planar flow casting technology yielded samples in a ribbon-form 2 mm wide and 20 m thick. The checked area chemical compositions were in agreement with the nominal ones. Nevertheless, the darker square objects and smaller bright objects observed at the wheel side of the Fe2MnSi ribbon sample yielded higher Mn content at the expense of Fe. The X-ray diffraction patterns of all samples have indicated L2(1) structure with lattice parameters, 0.567 (1) nm for Fe2MnSi and 0.584 (1) nm for Fe2MnAl, being within an experimental error independent of production technology. On the other hand, the technology has markedly influenced the microstructure clearly pointing to the larger size of grains and grain boundaries in the disc samples. From the magnetic viewpoint, both alloys are paramagnetic at room temperature without visible influence of their production. On the contrary, the low-temperature behavior of the microscopic hyperfine parameters and the macroscopic magnetic parameters exhibits differences affected by both chemical composition and microstructure.Web of Science125art. no. 71

Full-scale magnetic, microstructural, and physical properties of bilayered CoSiB/FeSiB ribbons

The paper is devoted to the detailed analysis of microstructural and magnetic properties of the as-quenched bilayered Co72.5Si12.5B15/Fe77.5Si7.5B15 ribbons prepared by the planar flow casting (PFC) method with single crucible. The interface between both amorphous Co- and Fe-based layers is not uniform and its thickness ranges from 0.5 to 6 μm over the whole ribbon length. Dependences of mechanical characteristics on the ribbon thickness show increase in Young’s modulus from 140 to 170 GPa and decrease in microhardness from 18 to 13 GPa, when measured from the wheel (Co) to air (Fe) side. By fixing the coiled ribbon on the planar sample holder a uniaxial magnetic anisotropy with the out-of-plane and the in-plane easy axis is induced on the air and wheel side, respectively. Bulk magnetic properties confirm that perpendicular anisotropy observed on the air side becomes stronger as getting deeper under the surface and overlaps the in-plane anisotropy from the wheel side. This is in good agreement with Mössbauer measurements. Magnetic characteristics (surface hysteresis loops and domains, bulk hysteresis loops and thermomagnetic curves) of the bilayered samples were further compared with the single-layered CoSiB and FeSiB alloys.Web of Science58169268

Magnetically modified nanogold-biosilica composite as an effective catalyst for CO oxidation

The temperature-dependent biosynthesis of gold nanoparticles (AuNP) using diatom cells of Diadesmis gallica was successfully performed. The resulting biosynthesis product was a bio-nanocomposite containing AuNP (app. 20 nm) subsequently anchored on the silica surface of diatomaceous frustules. As-prepared nanogold-biosilica composite was tested as catalyst in the oxidation of carbon monoxide using gas chromatograph with thermal conductivity detector. For catalytic activity enhancement, bionanocomposite was magnetically modified by ferrofluid using two different methods, i.e., with and without the use of methanol. The oxidation of CO at 300 degrees C was 58-60% in the presence of nanogold-biosilica composites. CO conversion at 300 degrees C was only 15% over magnetically responsive sample modified in the presence of methanol. On the other hand, complete CO conversion was reached over direct (without methanol) magnetically modified nanogold-biosilica composite at 330 degrees C (GHSV = 60 l g(-1) h(-1)). Our results show, that the type of magnetic modification can influence the catalytic activity of bionanocomposite. The best catalytic effect in CO conversion established direct magnetically modified nanogold-biosilica composite.Web of Science1271158114

Influence of heat treatment on the structural and magnetic characteristics of (NdxPr1-x)(2)Fe14B-based magnetic material for low-temperature application

Sintered Pr-Nd-Fe-B-based permanent magnets with 10 and 13 wt. % of Pr were prepared by traditional technology and then subjected to various heat treatments. Stoichiometric composition of the matrix grains corresponds to (Pr0.3Nd0.7)2Fe14B and (Pr0.4Nd0.6)2Fe14B compounds, respectively. Conducted thermomagnetic analysis to samples of these magnets showed the presence of spin-reorientation transition in temperature 95 and 75 K, respectively. This makes the magnet potentially applicable for low temperatures. For these compounds, we have determined the optimum heat-treatment conditions. The magnetic domain structure of the magnet subjected to an optimum heat treatment has been studied. The effect of different low-temperature heat treatments on the magnetic properties of magnets has been demonstrated.Web of Science55462462

Polarimetry of optical and magneto-optical systems

Import 15/01/2007PrezenčníNeuveden

Šíření světla v tlustých magneto-optických vrstvách

Import 20/04/2006Prezenční výpůjčkaVŠB - Technická univerzita Ostrava. Fakulta elektrotechniky a informatiky. Katedra (454) elektroniky a telekomunikační technik

Influence of tensile stress on the surface magneto-optical hysteresis loops in amorphous and (nano)crystalline ribbons

The behavior of the surface magnetic anisotropy in the amorphous and (nano)crystalline ribbons is investigated using the magnetooptical (MO) methods. In this paper, the differential intensity MO method is extended by the specially designed sample holder suitable for applying the tensile stress in the ribbon axis. Measured surface hysteresis loops, represented as a function of tensile stress σ, offer an interesting insight into the magnetoelastic properties of the ribbon surface phases. These dependencies are studied and discussed in the case of the surface-crystallized Co66Fe4Si15B15 and the as-quenched amorphous Fe77.5Si7.5B15 ribbons. It is shown that the response of the surface crystalline phases and the amorphous matrix on applied stress is significantly different. This is manifested by the changes in the value and sign of magnetostriction coefficient λs. Good agreement between the surface and bulk magnetostriction is obtained for the FeSiB ribbons that are amorphous in the volume as well as on the surface.Web of Science504art. no. 200280