Arcady Zhukov

Thin Magnetically Soft Wires for Magnetic Microsensors

Recent advances in technology involving magnetic materials require development of novel advanced magnetic materials with improved magnetic and magneto-transport properties and with reduced dimensionality. Therefore magnetic materials with outstanding magnetic characteristics and reduced dimensionality have recently gained much attention. Among these magnetic materials a family of thin wires with reduced geometrical dimensions (of order of 1–30 μm in diameter) have gained importance within the last few years. These thin wires combine excellent soft magnetic properties (with coercivities up to 4 A/m) with attractive magneto-transport properties (Giant Magneto-impedance effect, GMI, Giant Magneto-resistance effect, GMR) and an unusual re-magnetization process in positive magnetostriction compositions exhibiting quite fast domain wall propagation. In this paper we overview the magnetic and magneto-transport properties of these microwires that make them suitable for microsensor applications.

Optimization of giant magnetoimpedance in Co-rich amorphous microwires

The dependences of the magnetoimpedance ratio /spl Delta/Z/Z of soft magnetic Co/sub 67/Fe/sub 3.85/Ni/sub 1.45/B/sub 11.5/Si/sub 14.5/Mo/sub 1.7/ glass-coated amorphous microwires with various geometric ratio /spl rho/ upon axial magnetic field H has been measured for the frequency f range 0.06-15 MHz, driving current amplitude I of 0.75-2 mA, and H up to 2400 A/m. Surface hysteresis loops have been measured by transverse magnetooptical Kerr effect (MOKE). A maximum relative change in the giant magnetoimpedance (GMI) ratio /spl Delta/Z/Z up to around 615% is observed at f=10 MHz and I=0.75 mA in the sample with /spl rho//spl ap/0.98. Application of dc bias current strongly affects the GMI ratio. A maximum of GMI ratio occurs approximately at the same field as the coercivity of surface loops.

Manipulation of domain wall dynamics in amorphous microwires through the magnetoelastic anisotropy

We studied the effect of magnetoelastic anisotropy on domain wall (DW) dynamics and remagnetization process of magnetically bistable Fe-Co-rich microwires with metallic nucleus diameters (from 1.4 to 22 μm). We manipulated the magnetoelastic anisotropy applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses. Microwires of the same composition of metallic nucleus but with different geometries exhibit different magnetic field dependence of DW velocity with different slopes. Application of stresses resulted in decrease of the DW velocity, v, and DW mobility, S. Quite fast DW propagation (v until 2,500 m/s at H about 30 A/m) has been observed in low magnetostrictive magnetically bistable Co56Fe8Ni10Si10B16 microwires. Consequently, we observed certain correlation between the magnetoelastic energy and DW dynamics in microwires: decreasing the magnetoelastic energy, Kme, DW velocity increases.

Effect of transverse magnetic field on domain wall propagation in magnetically bistable glass-coated amorphous microwires

We experimentally studied domain wall (DW) propagation in amorphous Fe69Si10B15C6 and Co56Fe8Ni10Si11B16 microwires. We found that, in some cases, application of transverse magnetic field increases DW velocity in studied microwires. This effect is explained considering effect of transverse magnetic anisotropy on DW propagation. Considerable increase of DW velocity has been observed at enhanced longitudinal magnetic field, H. Such abrupt increasing of DW velocity can be related with defects contribution.

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.

The comparison of direct and indirect methods for determining the magnetocaloric parameters in the Heusler alloy Ni50Mn34.8In14.2B

The magnetocaloric properties of the Ni50Mn34.8In14.2B Heusler alloy have been studied by direct measurements of the adiabatic temperature change (ΔTAD(T,H)) and indirectly by magnetization (M(T,H)), differential scanning calorimetry, and specific heat (C(T,H)) measurements. The presence of a first-order ferromagnetic-paramagnetic transition has been detected for Ni50Mn34.8In14.2B at 320 K. The magnetocaloric parameters, i.e., the magnetic entropy change (ΔSM = (2.9-3.2) J/kgK) and the adiabatic temperature change (ΔTAD = (1.3-1.52) K), have been evaluated for ΔH = 1.8 T from CP(T,H) and M(T,H) data and from direct ΔTAD(T,H) measurements. The extracted magnetocaloric parameters are comparable to those of Gd.

Evaluation of the saturation magnetostriction in nearly zero magnetostrictive glass-coated amorphous microwires

Measurements of the saturation magnetostriction λs of glass-coated covered (Co1−xMnx)75Si10B15 (x=0.09, 0.10 and 0.105) and Co56.5Fe6.5Ni10B16Si11 amorphous microwires carried out by means of the stress dependence of initial magnetic susceptibility method are reported. The conditions of applicability of this method to the microwires have been analyzed, taking into account the domain structure expected for very low negative magnetostriction of the metallic nucleus. The experimental data of λs obtained in those amorphous microwires are in agreement with those reported in amorphous ribbons with similar compositions.

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%.

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.

Dynamic coercive field of bistable amorphous FeSiB wires

The dynamic coercive field and area of the hysteresis loop A have been measured for bistable amorphous FeSiB wire as functions of frequency f and amplitude of an applied magnetic field. The results are presented in the form , . The values of the exponents m, p, x and z are given for an as-quenched wire with applied tension and without tension, and for an annealed wire with applied tension. The range of frequency f is from 0 to 700 Hz, and the range of amplitude is from 0 to 140 A . The exponents vary from 0.22 to 0.86. Differences are found for the first time between m and p, and between x and z. For higher frequencies (f >150-350 Hz) the bistable remagnetization process is not complete. Observed values of the exponents can be partially understood in terms of an equation of motion of reversible displacement of domain walls for the case of a small restoring force.