The values of the magnetostriction constant, l s , of Co-based glass-coated microwires have been investigated by using the small-angle magnetization rotation (SAMR) method. Performing the systematic measurements, we were able to choose the appropriate measurement conditions achieving a highprecision result. From the dependence of the evaluated magnetostriction coefficient on annealing conditions, we evaluated the influence of the internal stresses on the magnetostriction coefficient value and the influence of the heat treatment on the magnetostriction coefficient of nearly zero magnetostrictive Co-based microwires. We observed changes of the magnetostriction value and sign after annealing. The maximum on the dependence of the magnetostriction coefficient on annealing time is explained considering superposition of the stress relaxation and ordering and beginning of the crystallization process.

The total magnetic charges of head to head domain walls, Q = 〈Mz〉 S, are measured for a family of amorphous glass‐coated Fe‐rich microwires by means of time integration of the electro‐motive force signals induced in a pick‐up coil wound around the wire. Here 〈Mz〉 is the average longitudinal wire magnetization and S is the cross‐section of the wire metallic core. The measured values of 〈Mz〉 = 1100–1200 emu/cm3 are close to the wire saturation magnetization. This means that Fe‐rich microwires of given family are nearly uniformly magnetized in its ground state, far from the wire ends. The characteristic width of the head to head domain wall is estimated to be δ ∼ (40–75) d, depending on the wall velocity, where d is the metallic core diameter. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The design and performance of a magnetometer based on the off‐diagonal GMI effect in Co‐rich glass‐coated microwire are presented. The sensing element of the magnetometer is a 10‐mm long piece of Co–Fe–Ni–B–Si–Mo microwire with a small pick‐up coil of 85 turns wounded around the microwire. The electronics with a feedback circuit is used to register an electromotive force proportional to the external magnetic field applied along the wire axis. In the absence of the feedback current the magnetometer is capable of measuring a narrow range of magnetic fields, ±3.5 μT, in the frequency range of 0–1 kHz, the level of the equivalent magnetic noise being about 10 pT Hz−1/2 at a frequency of 300 Hz. The use of the feedback circuit increases the range of the measured magnetic fields up to ±250 μT. Photo of the giant magnetoimpedance magnetometer based on the off‐diagonal GMI effect in Co‐rich glass‐coated microwire.

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The hysteresis losses of a dense assembly of magnetite nanoparticles with an average diameter D = 25 nm are measured in the frequency range f = 10 – 200 kHz for magnetic field amplitudes up to H0 = 400 Oe. The low frequency hysteresis loops of the assembly are obtained by means of integration of the electro-motive force signal arising in a small pick-up coil wrapped around a sample which contains 1 – 5 mg of a magnetite powder. It is proved experimentally that the specific absorption rate diminishes approximately 4.5 times when the sample aspect ratio decreases from 11.4 to 1. Theoretical estimate shows that experimentally measured hysteresis loops can be approximately described only by taking into account appreciable contributions of magnetic nanoparticles of both very small, D < 10 – 12 nm, and rather large, D > 30 nm, diameters. Thus the wide particle size distribution has to be assumed

An adequate description of the results of experimental measurement of both diagonal and off-diagonal Giant magneto-impedance (GMI) components has been obtained for Co-rich amorphous microwire at moderate frequencies assuming the existence of a small off-diagonal tensor component of the residual quenching stress. The latter is the origin of a weak helical anisotropy of amorphous microwire. The micromagnetic simulation of the magnetization reversal process in the microwire under the influence of the applied magnetic field and dc bias current has been carried out. It is shown that due to the influence of the magneto–elastic interaction in a wire with a weak helical anisotropy, the behavior of the longitudinal and circular magnetization components is significantly correlated. Namely, the change of the sign of the longitudinal magnetization component under the influence of the axial magnetic field leads to a subsequent jump of the circular magnetization component at some critical value of the applied magnetic field. As a result of the jump of the circular magnetization, the off-diagonal GMI component also changes sign during the wire magnetization reversal. This effect is confirmed experimentally for a Co-rich wire with a small negative magnetostriction. It is also shown that the jump of the circular magnetization can be eliminated by a circular magnetic field of a weak dc bias current flowing along the wire. This effect allows one to design sensitive magnetic field sensor based on the measurement of the off-diagonal GMI component.

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