- [Show abstract] [Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
- [Show abstract] [Hide abstract] ABSTRACT: A novel magnetic field sensor, based on the giant magneto-impedance effect is described and analysed. The sensor utilises an annealed amorphous wire that can be up to 10 m long, and integrates the field over the length of the wire. It operates in an open-loop mode. With a bias field of 500 A/m, it achieves a sensitivity of 0.02 A/m and linearity of better than 5% for external fields between ±300 A/m.
- [Show abstract] [Hide abstract] ABSTRACT: The influence of domain wall movements in the giant magnetoimpedance measured in low magnetostrictive alloys has been studied. Samples were field annealed under a static field that was applied making an angle theta, varied from 90 deg to 0 deg, with the longitudinal ribbon axis. Measurements were performed up to 10 MHz. Obtained results and theoretical predictions are compared and discussed.
- [Show abstract] [Hide abstract] ABSTRACT: The field dependence of the Young's modulus (ΔE effect) has been studied in amorphous microwires, with their glass cover and after glass removal, and magnetic fibres based on Fe. The study of the ΔE effect can provide valuable information about the domain structure and internal stresses in these samples. The different magnetization processes in this kind of small sized samples are also discussed.
- [Show abstract] [Hide abstract] ABSTRACT: The field-dependence of magnetization, Young's modulus and magnetostriction have been used to investigate the domain structure of FeSiB amorphous wires. The experimental observations of the as-cast wire are explained in terms of a modified core-shell model in which the shell is magnetized in a series of domains oriented approximately perpendicular to the wire axis and the magnetization in the core is oriented at an average angle of about 44 degrees to the wire axis. The presence of reverse spike domains in the core at the ends of the wire is also suggested. The critical length below which magnetic bistability is lost may be associated with these reverse domains. The behaviour of wires annealed at 425 degrees C can be interpreted in terms of a similar model, except that the core volume and the length of the reverse spike domains are increased and the average magnetic moment angle in the core is decreased.
- [Show abstract] [Hide abstract] ABSTRACT: The dependence of magnetoimpedance (MI) on transverse susceptibility in soft ferromagnets is used in conjunction with an existing phenomenological domain structure model to study the relative importance of moment rotation and domain-wall motion in MI. It is shown that moment rotation is predominantly responsible for the observed behavior in amorphous wires at frequencies above 1 MHz. It is also necessary to include anisotropy distributions in both magnitude and direction. © 1998 American Institute of Physics.
- [Show abstract] [Hide abstract] ABSTRACT: The anhysteretic behaviour of nickel has been studied by two methods: the conventional field cycling method, and by thermal demagnetization followed by cooling in an applied field. The results show that the field cycling method does not achieve thermal equilibrium, the anhysteretic magnetizations differing by as much as 6% between the two methods. The results are discussed in terms of domain wall pinning
- [Show abstract] [Hide abstract] ABSTRACT: The tensile stress dependence of magneto-impedance (MI) in CoSiB and CoFeSiB amorphous wires is reported. A phenomenological model for the transverse susceptibility based on a simple domain structure, and which includes the magneto-elastic energy contribution, is used. The square-root of the transverse susceptibility is assumed to be proportional to the magneto-impedance. The model predicts correctly the form of the stress dependence of the MI-effect, and shows that a significant distribution in the magnitude of the anisotropy constant is needed to explain the MI-response of these wires. Modelling also suggests that at higher excitation frequencies (⩾1 MHz) magnetic moment rotation is the dominant process controlling the MI-effect
- [Show abstract] [Hide abstract] ABSTRACT: CoSiB wire at a range of stress levels. Fig. 2 shows the magnetic field dependence of the real component of the impedance of AQ-CoFeSB wire at a range of stress levels at 1 MHz . The reactance is typically an order of magnitude smaller than the resistance at 1 MHz. The magnetic field dependence of the reactance has a similar form to the resistance for both compositions, except that the reactance peak occurs at a higher magnetic field. From M(H) behaviour and phenomenological modelling the magneto-impedance response of the wires can be understood in terms of a two stage process. The impedance increase from zero field to the peak is due to an increase in the rotational transverse susceptibility resulting fiom the rotation of the magnetization towards the wire axis. The subsequent impedance decrease is attributable to an increasing axial field imposed ‘anisotropy’, which reduces the rotational susceptibility. Axial stress alters the magnitude and position of the impedance peak as the magnetoelastic anisotropy increases. The increasing magnetoelastic anisotropy shifts the peak to larger fields, the effect is greater for the CoSB wire which has larger magnetostriction. The influence of stress on the amplitude of the impedance response is more complex , reflecting an initial increase in the average easy axis angle (from the wire axis) and a sustained increase in the magnetoelastic anisotropy. On the basis of this understanding the MI response can be modified by controlled stress relief of the internal stresses through annealing.
- [Show abstract] [Hide abstract] ABSTRACT: A state-of-the-art scanning Hall probe microscope (magnetic field sensitivity : spatial resolution: 30 nT/sqrt(Hz):0.8 μm-300 nT/sqrt(Hz):0.25 μm) has been used to image a range of ferromagnetic media. The technique is non-invasive and yields quantitative profiles of the stray fields near the sample surface as illustrated by images of a standard magnetic reference sample, permalloy nanostructures and colossal magnetoresistive perovskites. Rapid scanning (~1 frame/12 sec) has also been used to study the domain reversal in a thin Ni film.
- [Show abstract] [Hide abstract] ABSTRACT: We report measurements of the ΔG effect and magnetomechanical damping in as-quenched and annealed amorphous wires of Co72.5Si12.5B15 having a saturation magnetostriction λs of about −3 × 10−6. Samples were measured in the as-quenched state, and after annealing at 450°C for times between 30 s and 1000 min. ΔG of up to 10% and magnetomechanical damping up to 0.004 have been found.
- [Show abstract] [Hide abstract] ABSTRACT: The field dependence of Young’s modulus (ΔE effect) of amorphous wires of Co 72.5 Si 12.5 B 15 has been studied in the as‐quenched state, and after annealing for times between one and several hundred minutes at temperatures of 450, 480, and 500 °C. In the as‐quenched state the ΔE effect is small (≪2%), because the quenching stresses couple with the magnetostriction (λ s ∼-3×10<sup>-6</sup>) to produce significant anisotropy. Annealing for short times (≳1 min) is sufficient to relieve much of the quenching stress, resulting in magnetic softening and enhanced ΔE effect (at best ≳30%). Further annealing eventually reverses these trends, increasing coercivity and anisotropy, and reducing the ΔE effect. This behavior is attributed to surface crystallization. The results are interpreted in terms of the core‐shell domain model, and are consistent with the retention of a significant component of circumferential domain structure in the shell in all annealing conditions studied. © 1996 American Institute of Physics.
- [Show abstract] [Hide abstract] ABSTRACT: The hard ribbon axis anisotropy induced in the magnetostrictive amorphous alloy Fe74.7Nb3Si12.8B9.5 by stress annealing at temperatures 633–693 K and under tensile stresses up to 204 MPa has been studied by several experimental methods (measurement of dc hysteresis loops, field dependence of engineering magnetostriction λe and Young's modulus E, and domain structure observations). The experimental data are discussed in terms of the phenomenological model developed earlier by Squire. The most significant improvement in the magnetoelastic response was found for the highest annealing temperature Ta = 693 K. The maximum ΔE effect (27%) observed is much lower than the maximum estimated theoretical value (87%). The λe and domain studies suggest that this difference is most probably due to the dispersion of easy axes and/or anisotropy values. Even though the phenomenological model does not take into account local variations in the anisotropy, it gives a reasonable quantitative description of a slightly perturbed hard ribbon axis case.
- [Show abstract] [Hide abstract] ABSTRACT: Magneto-impedance and ΔE measurements of amorphous wires having the compositions Fe<sub>77.5</sub>Si<sub>10</sub>B<sub>15</sub> and Co<sub>72.5</sub>Si<sub>12.5</sub>B<sub>15</sub> in the as-quenched and annealed states are presented. The results are interpreted in the light of the widely accepted core-shell domain models for positively and negatively magnetostrictive amorphous wires respectively. It is concluded that in wires of Fe<sub>7.5</sub>Si<sub>10</sub>B<sub>15</sub> the radial easy axis structure in the shell of the as-quenched wire weakens after light annealing, eventually giving way to a circumferential structure when surface crystallization occurs. In wires of Co<sub>72.5</sub>Si<sub>12.5</sub>B<sub>15</sub> significant circumferential anisotropy is inferred in all states of annealing studied
- [Show abstract] [Hide abstract] ABSTRACT: The magnetostrictive and magnetoelastic properties of amorphous wires produced by rapid quenching in rotating water are reviewed, with particular reference to the domain structure. Saturation magnetostriction and engineering magnetostriction of as-quenched and annealed wires having compositions of the type Fe/sub x/Co/sub 1-x/Si/sub y/B/sub 15/ (y=7.5-15) are discussed. The magnetoelastic properties reviewed are the field-dependent Young's modulus and shear modulus (/spl Delta/E and /spl Delta/G effects) and magnetomechanical damping (internal friction).< >
- [Show abstract] [Hide abstract] ABSTRACT: Measurements of the field dependent Young's modulus with resolution of parts in 106 allow domain processes to be studied in a novel way. Examples are given of the use of the technique for studying amorphous (Fe0.06Co0.94)72.5Si12.5B15 wires and the evolution of the nanocrystalline phase in Fe73.5Cu1Nb3Si13.5B9 ribbons.
- [Show abstract] [Hide abstract] ABSTRACT: Domain structures have been observed by the Bitter colloid method on the surface of as-cast FeSiB and FeCoSiB amorphous wires and annealed FeSiB amorphous wires. The domain patterns of the as-cast wires are complex but become simplified with progressive annealing as the internal stress is relieved.
University of Bath
Bath, England, United Kingdom
- Department of Physics