Search

Research was conducted on the influence of furnace annealing and crystallization on themagnetic and magnetoelastic properties of Fe-Si-B amorphous wire. Young's modulus and magnetization field dependence along with x-ray analysis and scanning electron microscopy were used to analyze annealing effects. Results suggested that progressive annealing causes relief of radial casting stresses, surface crystallization and bulk material crystallization.

The circumstances involved in the occurrence of magnetic induction changes and the primary qualitative characteristics of this phenomena were studied. Experiments were carried out in a uniaxial field and stress rig and involved the application of magnetic field and tensile or compressive stresses to the samples. The non-dependence of the principal anhysteric in a ferromagnet to specific material patrameters was demonstrated.

Magnetomechanical damping in FeSiB amorphous wires as a function of surface torsional strain was investigated. The results showed that the main driving mechanism for magnetomechanical damping was magnetomechanica hysteresis related with the movement of the 90 degree domain walls. Furnace annealing treatment at zero field effectively reduced the casting stress to around 2 MPa and resulted in slight surface crystallization.

Several studies have examined the effects of stress on the magnetic properties of ferromagnetic materials. Pravdin considered the effects of low-magnitude cyclic stress, separating irreversible and reversible changes following several cycles. The work is extended to higher magnitude stresses, and it is shown how the peak position of DeltaMIRR alters with the magnitude and sign of the applied stress, in a sample of 99.99% pure iron.

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.

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 ([greater than or equal to] 1 MHz) magnetic moment rotation is the dominant process controlling the MI-effect.

Amorphous metallic [Fe.sub.78][Si.sub.9][B.sub.13] fibers, 50 [[micro]meter] in diameter, produced by the melt extraction method, have been studied in the as-quenched state and after furnace annealing at 455 [degrees] C and 480 [degrees] C for times between 0.5 min and 50 min. Measurements of the M-H loops and field dependence of Young's modulus have shown that they behave in a way very like that of amorphous wires. The minimum coercivity of 3 A/m is greater than that found in wires, and the minimum Young's modulus ([approximately]0.45 times the saturation value) is greater. It is suggested that the core-shell domain model applies in the as-quenched state and that stress relief followed by surface crystallization dominate the anisotropy.

The field dependence of Young's modulus has been measured in samples of [Fe.sub.66][Cr.sub.8][Cu.sub.1][Nb.sub.3][Si.sub.13][B.sub.9] alloy annealed to induce varying nanocrystalline fractions. The results are interpreted partly in terms of internal stress relief and reduced magnetostriction in the nanocrystalline samples. It is necessary to invoke magnetocrystalline anisotropy within the nanocrystalline grains to explain the behaviour after annealing at higher temperatures and for longer times.

Changes in engineering magnetostriction, [[Lambda].sub.e] with annealing of undrawn furnace-annealed iron-based amorphous wires are presented. The peak [[Lambda].sub.e] falls initially due to progressive stress relief. With further annealing surface crystallization is initiated and increases, leading to an increase in the peak [[Lambda].sub.e]. The peak [[Lambda].sub.e] approaches the theoretical maximum, corresponding to an easy axis of magnetization oriented perpendicular to the wire axis, after annealing for sixty minutes at 470 [degrees] C.

The magnetic field dependence of Young's modulus is a useful technique for probing the magnetic moment configuration and the anisotropy energy density of magnetostrictive soft magnetic materials. More recently, a high resolution vibrating reed system, based on the closed loop operation of an analogue lock in amplifier (LIA), coupled with an analogue voltage controlled oscillator (VCO) has been used. This system has shown that such measurements are capable of providing new information about subtle domain rearrangements during magnetisation of as-cast amorphous wires. The performance of this system is limited by the rise of the analogue components, especially the VCO, to a resolution of a few parts in [10.sup.5]. To overcome this limitation a digital LIA and a function generator which employs digital frequency synthesis methods have been used in a new system. This offers an order of magnitude reduction in noise, with a frequency stability of better than [10.sup.6] Hz, which can provide a resolution better than 2 parts in [10.sup.6] for Young's modulus. Examples of data obtained are included.

The induction changes caused by the application of tensile and compressive stress cycles from points on the initial curve and major loop of a 0.2% carbon, 3% nickel steel have been measured using a pneumatic stressing mechanism. The magnitudes of the irreversible induction changes are compared to the specimen iso-stress permeability and Barkhausen profiles. Results suggest that the complexity of the induction-stress process limits the suitability of either profile as a suitable 'response function' for the prediction of subsequent stress-induced induction changes.

The field dependence of Young's modulus, E(H), of as-cast Fe-based amorphous wire has been investigated using a new high resolution vibrating reed system. The E(H) data have been combined with dc M(H) loops and Kerr effect surface domain images to provide new information about the effect of the large Barkhausen jump which characterizes the magnetization reversal in this material. At low-fields the modulus decreases via an abrupt small step which correlates with the field at which the large Barkhausen jump occurs in the M(H) behaviour. It is suggested that the reversal of the magnetization in the core domain leads to a slight rearrangement of domains in the sheath region of the wires. This is supported by the surface domain images and indicates a small asymmetry in the remanence states.

The magnetic field dependence of magnetization and Young's modulus of pulse-annealed Fe77.5Si7.5B15 are reported. Coercivity and anisotropy energy density were measured as a function of annealing current and the tensile stress applied during annealing. It is shown that pulse annealing can remove the internal stresses more effectively than furnace annealing. Coercivity and anisotropy energy density fall by a few percent for annealing currents up to 1 A. Currents between 1 A and 1.5 A reduce both quantities by nearly an order of magnitude. Higher annealing currents result in sharp increases in the parameters, as crystallization begins.

Measurements of the field-dependent magnetostriction and delta-E effect in annealed, cold-drawn amorphous wires, 90 micrometer in diameter, are reported. The results are discussed in the light of existing domain models. Annealing first reduces the anisotropy; further annealing in air induces surface crystallization. It is suggested that this favours a circumferential domain structure, favourable for large magnetoelastic effects.

Studies the significance of the role of moment rotation and domain-wall motion in magnetoimpedance (MI) in soft ferromagnets. Relationship between the domain structure and anisotropy and magnitude of the MI; Changes that occur in amorphous wires at frequencies above 1 megahertz; Results of this study.