A. Talaat

Magnetostriction of Co–Fe-Based Amorphous Soft Magnetic Microwires

We studied the correlation between magnetic softness and magnetostriction coefficient for as-prepared and annealed Co–Fe-rich microwires. We found that the hysteresis loops and magnetostriction coefficients of Co and Fe-rich microwires depend not only on the chemical composition of the metal but also on internal stress. Consequently, both hysteresis loop and magnetostriction coefficient can be adjusted by annealing. We varied the time and temperature of annealing and observed changes of the character of the hysteresis loops. These changes correlated with evolution of the magnetostriction coefficient. Drastic changes of the hysteresis loop for Co-rich microwires were attributed to changes of the sign and value of the magnetostriction coefficient.

Optimization of the giant magnetoimpedance effect of Finemet-type microwires through the nanocrystallization

We studied correlation of magnetic properties, giant magnetoimpedance (GMI) effect and structure of Finemet-type glass-coated microwires obtained by the Taylor-Ulitovski technique. We observed considerable magnetic softening and increasing of the GMI ratio, ΔZ/Z, (from 3% up to 100%) after annealing of studied microwires. On the other hand, even in as-prepared Fe73.8Cu1Nb3.1Si13B9.1 microwire, we observed existence of α-Fe nanocrystallites with average grain size about 12 nm and considerable GMI effect (ΔZ/Z up to 50%).

Tailoring of domain wall dynamics in amorphous microwires by annealing

We studied the effect of annealing on the magnetic properties and domain wall (DW) dynamics of magnetically bistable, Fe-based, glass-covered microwires with two different compositions, and different diameters. We observed the correlation of the domain wall dynamics with the distribution of the nucleation fields, measured in as-prepared samples, and after annealing for up to 150 min at temperatures of 250 and 300 °C. We found that both DW velocity and the range of the field limiting the single DW dynamics changed after annealing.

Tailoring the High-Frequency Giant Magnetoimpedance Effect of Amorphous Co-Rich Microwires

We studied the giant magnetoimpedance (GMI) effect and magnetic properties of amorphous Co-rich magnetic microwires prepared by the Taylor-Ulitovski technique. The magnetic field dependence of impedance and the magnetic anisotropy fields can be tailored through the magnetoelastic anisotropy by controllable change of the internal stresses. Co-rich microwires exhibit high (above 300) GMI effect even at gigahertz frequencies. Features of the high-frequency GMI effect were analyzed using a ferromagnetic resonance-like approximation.

Effect of Nanocrystallization on Magnetic Properties and GMI Effect of Fe-rich Microwires

We studied the giant magnetoimpedance (GMI) effect and magnetic properties of Finemet-type FeCuNbSiB microwires. We observed that the GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored by controlling the magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires, and can also be considerably improved either by heat treatment and/or choosing the suitable fabrication conditions. We observed a considerable magnetic softening of the microwires after the appropriate annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous Fe-rich microwires exhibited a low GMI effect (GMI ratio below 5%). A considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat-treated microwires with nanocrystalline structure.

Effect of Nanocrystallization on Magnetic Properties and GMI Effect of Microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of FINEMET-type FeCuNbSiB microwires. We observed that the GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored either controlling magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires or controlling their structure by heat treatment or changing the fabrication conditions. We observed considerable magnetic softening of studied microwires after annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous microwires exhibited low GMI effect (GMI ratio below 5%). Considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat treated microwires with nanocrystalline structure. Some of as-prepared Fe-rich exhibited nanocrystalline structure and the GMI ratio up to 45%.

Influence of the defects on magnetic properties of glass-coated microwires

We observed different kind of defects, such as gas bubbles, glass coating thickness inhomogeneities, indications of the chemical interaction between the glass shell and the metallic nucleus. We showed that the existence of such bubbles might be the origin of the spontaneous fluctuations of the local nucleation field.

Giant magnetoimpedance effect and domain wall dynamics in Co-rich amorphous microwires

The giant magnetoimpedance (GMI) effect, as well as the magnetic and magneto-optical properties, of Co69.2Fe4.1B11.8Si13.8C1.1 and Fe73.8Cu1Nb3.1B9.1Si13 amorphous microwires is studied. It is observed that the magnetic properties and the GMI effect of the Co-rich microwire can be tuned by heat treatment. A high GMI effect has been observed in as-prepared Co-rich microwires. After appropriate annealing of the Co-rich microwires, fast domain wall propagation and a GMI effect can be simultaneously observed in the same sample, and annealing is seen to affect both the diagonal and off-diagonal GMI components. Using complementary studies of the bulk and surface magnetic properties, an attempt is made to explain the great difference observed in the GMI properties of Co- and Fe-based microwires exhibiting very similar bulk hysteresis loops.

Tuning of Magnetic Properties and GMI Effect of Co-Based Amorphous Microwires by Annealing

We studied the effect of annealing on the giant magnetoimpedance (GMI) effect, magnetic domain wall dynamics, and magnetic properties of amorphous iron (Fe) and cobalt (Co)-based microwires prepared by the Taylor–Ulitovsky technique. We observed that the properties can be tailored by controlling the magnetoelastic anisotropy of CoFeBSiC microwires during wire formation and also controlling the magnetic anisotropy by further heat treatment. A high GMI effect has been observed in the as-prepared Co-based microwires. High domain wall velocity and rectangular hysteresis loops have been observed in additionally heat-treated microwires. We observed increasing of the wall velocity under stress in some annealed samples. We demonstrated that, for certain annealing conditions, we can observe coexistence of the GMI effect and magnetic domain wall propagation in the same sample.

Studies of High-Frequency Giant Magnetoimpedance Effect in Co-Rich Amorphous Microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of various Co-rich amorphous microwires. We measured the values of magnetic field dependence of the GMI ratio up to gigahertz frequency range, and observed quite high GMI ratio in as-prepared Co-rich microwires even at gigahertz frequencies. We observed the different values of the magnetic anisotropy field obtained from the hysteresis loops and the impedance curves. Observed dependence can be explained considering different magnetic anisotropy in the surface layers and in the inner part of metallic nucleus and skin depth effect. Features of high-frequency GMI effect have been analyzed using ferromagnetic resonance-like approximation.