Tibor-Adrian Óvári

Magnetic behavior of negative and nearly zero magnetostrictive glass-covered amorphous wires

Results on the magnetic behavior and properties of negative and nearly zero magnetostrictive amorphous glass-covered magnetic wires and on their changes determined by glass removal, applied tensile stresses, and annealing are reported. The experimental data allow the explanation of their specific magnetic behavior as emerging from the changes produced in the domain structure by these factors. The similarity in behavior between negative and nearly zero magnetostrictive glass-covered wires is due to the very high values of internal stresses induced during preparation.

Domain Wall Propagation in Nearly Zero Magnetostrictive Amorphous Microwires

Results on the investigation of the propagating 180deg domain walls in bistable amorphous glass-coated microwires with nearly zero magnetostriction are reported for the first time. As-cast glass-coated microwires are bistable only if their metallic nucleus diameter is larger than 20 mum. Glass removal induces bistability in microwires with metallic nucleus diameters below 20 mum. Nearly zero magnetostrictive glass-coated microwires display larger domain wall velocities and mobilities as compared to positive magnetostrictive microwires. Samples that become bistable after glass removal display smaller values of the wall mobility as compared to as-cast bistable microwires. Mobility can be increased by annealing. The experimental results have been explained based on the damping mechanisms of the domain wall motion, specifically on the spin relaxation damping, whose coefficient is proportional to the anisotropy constant from the microwires inner core. Stress relief determined by glass removal and annealing have been considered. The results are important for future applications of nearly zero magnetostrictive microwires in spintronic devices.

Domain wall velocity in submicron amorphous wires

Results on the study of the domain wall propagation in rapidly quenched submicron amorphous wires with positive and nearly zero magnetostriction are reported. Samples with metallic nucleus diameters between 350 and 950 nm have been analyzed. A correlation between the magnitude of the uniaxial anisotropy and the domain wall velocity has been found. The largest wall velocity value was 1600 m/s, close to the largest values reported in typical microwires with the same composition. Wall mobility increases as the metallic nucleus diameter decreases due to the crucial role played by shape anisotropy in such ultrathin wires. Magnetoelastic anisotropy still has an important contribution in positive magnetostrictive samples. The maximum velocity values are obtained in nearly zero magnetostrictive wires at much smaller fields compared to positive magnetostrictive ones.

Comparative study of the magnetic properties of positive and nearly zero magnetostrictive submicron amorphous wires

Rapidly solidified submicron amorphous wires with positive and nearly zero magnetostriction are studied in order to understand the effect that a significant reduction in the diameter of the metallic nucleus has on their magnetic behavior and anisotropy distribution. Submicron wires with metallic nucleus diameters between 350 and 800 nm were investigated with hysteresis loop measurements, the magneto-optical Kerr effect, and ferromagnetic resonance studies. The analysis of the results shows the dominant role of shape anisotropy in nearly zero magnetostrictive submicron wires, as well as in positive magnetostrictive ones with nucleus diameters smaller than 350 nm. Magnetoelastic anisotropy is still important in positive magnetostrictive submicron wires with metallic nucleus diameters larger than 500 nm.

Magnetic Characterization of Submicron Wires and Nanowires Using Digital Integration Techniques

A new procedure for performing magnetic measurements on a single ultrathin magnetic wire is presented. The proposed solution is based on the use of digital integration techniques. Such a new measuring method was required by the recent development of novel magnetic materials such as rapidly solidified amorphous nanowires and submicron wires, for which a fast and reliable method of measuring the axial hysteresis loop was lacking. The new procedure implies two methods of measuring the hysteresis loop: one which requires a large number of measurements in order to determine the profile of the hysteresis loop, and another one which removes all the noise from rectangular loops associated with magnetically bistable samples. The first method can be employed for any ultrathin wire shaped sample, while the second one is suitable only for bistable samples with rectangular hysteresis loops, although it is ultrafast.

Domain Wall Propagation in Nanocrystalline Glass-Coated Microwires

The characteristics of domain wall propagation in Fe73.5Cu1Nb3Si13.5B9 amorphous and nanocrystalline glass-coated microwires are investigated in order to determine the changes induced by structural transformation in wall velocity and mobility. An improved method for sensing the wall presence and direction, and for measuring its velocity, is also presented. Amorphous samples are bistable, and their wall velocity displays typical values for microwires with positive magnetostriction. Nanocrystallized samples are not bistable in general, but they become bistable either if the glass coating thickness is large enough to induce a strong axial anisotropy, or if their metallic nucleus diameter is large enough to increase the contribution of the magnetostatic term. Bistable nanocrystalline microwires display smaller switching field values, together with larger wall velocity and mobility values as compared to bistable amorphous samples with the same composition. The results have been explained considering the changes induced in magnetostriction by the nanocrystalline phase formation and the magnetization reversal mechanism by means of wall propagation.

Giant magneto-impedance effect in soft magnetic wire families

Summary form only given. The giant magneto-impedance (GMI) effect-an abrupt change in the high frequency impedance of a magnetic conductor subjected to a relatively small dc magnetic field-has been widely studied in the last several years. GMI effect investigations performed on various soft magnetic wire families have demonstrated that such materials are very appropriate for microsensor applications based on this effect. The aim of this paper is to review the most recent advances in the field of the GMI effect in soft magnetic wire shaped materials, such as conventional amorphous wires prepared by in rotating-water quenching, nanocrystalline wires prepared from amorphous precursors, amorphous glass-coated microwires, and nanocrystalline glass-coated microwires.

Switching field calculations in amorphous microwires with positive magnetostriction

Abstract A new method for the calculation of switching field values in Fe 77.5 Si 7.5 B 15 amorphous microwires with large and positive magnetostriction is presented. The approach used is based on the nucleation at coercivity process. The anisotropy constants that enter the energy balance are calculated starting from internal stresses induced during preparation. Experimental values of the switching field are used to validate the theoretical results.

Correlation between the magneto-impedance and ferromagnetic resonance responses in nanocrystalline microwires

Results on the correlation between ferromagnetic resonance and magneto-impedance responses in soft magnetic Fe-based microwires with nanocrystalline structure are reported for the first time. The evolution of the magneto-impedance effect with structural changes starting from the as-cast amorphous state up to nanocrystallization and further crystallization is interpreted through changes induced in the surface magnetic anisotropy and magnetization process of such wires, that are studied by means of ferromagnetic resonance.

FMR Investigation of the nanocrystalline FeCuNbSiB glass-covered wires

Abstract The evolution of magnetic anisotropy and magnetization mechanisms during nanocrystalline phase formation and crystallization of Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 glass-covered wires are studied by ferromagnetic resonance. The modifications of the magnetic anisotropy due to structural changes are determined from the main resonance peaks. Changes in the magnetization processes are revealed by the low field peaks detected for all samples.