N. Bayri

The effect of furnace annealing and surface crystallization on the anisotropy, ΔE and magnetoimpedance effects in Fe71Cr7Si9B13 amorphous wires

The dependence of the magnetization loops, coercivity, anisotropy constant, ?E and magnetoimpedance (MI) effects in positively magnetostrictive Fe71Cr7Si9B13 amorphous wires on annealing conditions were studied. Samples were annealed at temperatures of 440?C and 460?C for durations between 0.3 and 300?min. The results indicate that progressive annealing first leads to relief of internal stresses and annealing of wires at 460?C for 60?min produces the minimum coercivity of about 1?A?m?1. Further annealing increases the coercivity and anisotropy, due to partial crystallization at the surface. It was found that the anisotropy changes its direction to the circumferential direction with the surface crystallization. The maximum change in Youngs modulus was measured to be about 75% in a partly surface crystalline sample. It was observed that the magnitude of the MI effect of the stress relieved sample could exceed 200% at 1?MHz.

Effect of tensile stress on magnetoimpedance properties of CoNiFe/Cu wire

AC o 20.5Ni40.5Fe39 magnetic film was electrodeposited onto a copper wire 50 µm in diameter. The magnetoimpedance (MI) effect, (�Z/Z) H(%) = ((Z(H ) − Zmax)/Zmax) × 100, was measured in the Co20.5Ni40.5Fe39/Cu composite wire under varying tensile stresses up to 30 MPa. The results showed that large MI and stress impedance (SI) effects can be observed in the Co20.5Ni40.5Fe39/Cu composite wire. The MI curve at zero tensile stress shows a small split peak in the low-field region. With increasing applied tensile stress, single-peak behaviour of the MI effect is observed. The magnitude of the MI and SI effects decreases with increasing tensile stress, σ . The peak values of (�Z/Z) H(%) for the sample decrease from 265% at σ = 0 to 39% at σ = 30 MPa at 40 kHz ac driving-current frequency. The impedance of a sample under the effect of 25 MPa tensile stress at 40 kHz ac driving-current frequency showed variations of about 146%. It was also found that the frequency value, f ∗ , where the maximum MI effect was observed as a function of driving-current frequency, increases with increasing tensile stress.

Investigation of a weak magnetic field effect on the in vitro catalytic activity of adenosine deaminase and xanthine oxidase.

The effect of a weak magnetic field (MF) on adenosine deaminase (ADA) and xanthine oxidase (XOD) activities have been investigated. A 50 Hz uniform MF was generated, and the magnitude of the field was kept constant at 5.8 mT. The changes in ADA activity over time were significantly different in and out of the MF; MF caused a steeper decline in ADA activity compared to the situation when no MF is present. In addition, MF caused a significant increase in XOD activity. There were no significant time-related changes for either enzyme in the absence of the MF. We suggest that a weak MF affects enzymatic systems.

The Dynamic Effects in Electrodeposited NiFe/Cu Wire with Preliminary Torsion

Ni80Fe20/Cu composite wires were produced under torsion using electrodeposition method. The total length of the magnetic film deposited onto 50 µm Cu wire is 3 cm and the thickness of the magnetic layer is about 10 µm. All samples showed single peak in magnetoimpedance (MI) curves. The magnitude (ΔZ/Z) % are 260%, 235% and 119% for samples produced under 22.4, 44.8, 89.7 rad/m torsion values, respectively at driving frequency of 160 kHz. MI effect magnitude decreases with increasing applied torsion during the electrodeposition process. A linear change in the second harmonics of output voltage from wire ends as a function of applied magnetic field (coil-less fluxgate effect) was observed in all sample. The sensitivity of coil-less output increases with increasing torsion and maximum sensitivity was observed in the sample produced at 89.7 rad/m torsion.