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Magnetic materials with very different saturation magnetostriction (lambda(s)) were selected: Co59Fe16Zr6CU1Nb2B16 amorphous alloy with low lambda(s) value (congruent to 10(-7)), Fe62.5Co6Ni7.5Zr7.5Cu1Nb2B15 amorphous alloy with lambda(s) congruent to 10(-5) and Tb0.27Dy0.73Fe2.0 (Terfenol) alloy with giant magnetostriction (lambda(s) congruent to 10(-3)). Magnetization intensity curves were obtained by means of a vibrating sample magnetometer from room temperature to 10 K. At low magnetizing field a reentrant magnetization behaviour was evidenced in all the investigated materials. This effect is proportional to magnetostriction value, going from a large effect in Terfenol to a small one in low magnetostriction materials. Saturation field, coercive field and hysteresis area behaviours as a function of temperature are in agreement with both the measured magnetization reentrance and stress-induced effects.

ypical Fe–Si sheets were cut using various techniques, reducing the material to ribbons having their grains oriented parallel to the longitudinal axis. The magnetic and magnetoelastic properties in this direction reveal differences in the effects produced by conventional mechanical cutting in comparison with laser cutting. In particular, the latter technique results in both the highest saturation magnetisation level and the lowest values of coercive field, hysteresis loss, and saturation magnetostriction. It can be inferred from the results that laser cutting is effective in decreasing both induced stresses and defects on the cut edges.MST/1446

A previos thermal model for the heat treatment of a little metal ribbon, moving under a broad laser beam with Gaussian intensity distribution, is elaborated in order to apply it also in the opposite experimental condition, namely for sample width higher than the laser spot. The temperature value vs. the distance from the symmetry axis of the treated zone is determined as a function of both the sample displacement rate and the laser power. When structural and magnetic-property modulation is produced in the transverse direction of a glassy metal ribbon, the experimental results, concerning both reduced magnetization as a function of the temperature and structure changes, are in agreement with the thermal-model predictions.

We have produced ribbons of Co1-xPx (x almost-equal-to 0.09) with the coexistence of microcrystalline and amorphous structure. These kind of materials have different magnetic and magnetostrictive behaviour in comparison with that already known of crystalline or amorphous specimens (x almost-equal-to 0.05 and 0.12, respectively). In particular we demonstrate the obtaining of good magnetoelastic response and, at the same time, the results validate the structure sensitivity of resonant magneto-acoustic waves. The complete behaviour of wave amplitude as a function of the applied magnetization field is compared for each sample and explained.

Mossbauer spectra, susceptibility and magnetization measurements were performed on Fe 40 Ni 40 P 14 B 6 amorphous ribbons. The results indicate the existence of correlated ferromagnetic regions of different sizes. With decreasing temperature a collective freezing of the resulting moments occurs with cluster-glass-like characteristics.

The behaviour of low field magnetization versus temperature is strictly dependent on phosphorus atomic fraction in Co 1− x P x alloys, namely on the structure of the material. In particular the presence of a transition to reentrant magnetization at low temperature is validate and its relation with the degree of disorder demonstrated.

Measurements of the initial permeability as a function of tensile stress were performed in cw-laser annealed metglas 2826 (50 μm ribbon). The results indicate the possibility of decreasing the magnetization at a very low field by means of an appropriate applied tension. The dependence of the magnetostriction curves and the magnetoelastic wave amplitude on the tensile stress supplies experimental evidence of the above mentioned prediction. On the basis of current understanding of the inhomogeneous mode of deformation, an explanation of the observed effects is proposed Mesure de la permeabilite magnetique initiale des rubans de 50 μm d'epaisseur recuits par laser continu en fonction de la traction. L'aimantation peut etre reduite. Courbes de magnetostriction et amplitude de l'onde magnetoelastique. Explication par un mode inhomogene de deformation

Laser annealing of amorphous alloy ribbons was performed by irradiating either their smooth or rough side. Experimental results such as hyperfine field distributions, average orientation of the magnetic moment, X-ray diffractography, initial permeability, magnetic anistropy, and low field magnetization, show the influence of the surface characteristics on the effects induced by the laser treatment. In particular, the effects of an applied tensile stress are compared to eachother and with previously obtained results. Many results are explained by means of the crystallization occurrence (at surface and also bulk) and taking into account its dependence on the irradiated surface properties and interaction time.

The magnetization changes, ΔM, induced by an external tensile stress, σ, in metallic-glass ribbons are theoretically calculated starting from the simplified model generally used for describing the magnetoelastic coupling in amorphous metals. Taking into account the discrepancies between the ideal behaviour and the real one as revealed in commercial amorphous ribbons, we show that the experimental results, concerning ΔM as a function of σ, can be well predicted by the theoretical evaluations. On the other hand, it results that a suitable ferromagnetic ribbon can be a magnetoelastic sensor able to measure variations of ≃1 MPa up to the 100 MPa stress.

The Young modulus dependence on thermal treatment and magnetization state was analysed on various metallic glasses. Propagation of standing magnetoelastic waves was used as an investigation technique. A simple model was elaborated to predict the magnetoelastic coupling. The explanation of the results was suggested on the basis of macroscopic and microscopic relaxation effects and is also revealed by the measurement of internal friction and magnetoelastic-coupling constant.

The as quenched amorphous ribbons are in a metastable condition and need a thermal treatment to relax internal stresses and/or to induce magnetic anisotropy. The evaluation of the results of various annealing treatments of the alloy Metglas 2826 was performed by magnetic measurements and Mossbauer spectroscopy, for the characterization of structural relaxation, easy magnetization axis changes and transition to crystalline order. Heat treatments considered include conventional (batch), laser and magnetic annealing (in transversal field).

The initial development of the transverse anisotropy induced by magnetic annealing is investigated for magnetizing field values which are much smaller than the ones generally employed. Measurements of Young modulus and longitudinal magnetostriction not only show their relation with induced anistotropy, as predicted in a previous paper, but also enable us to calculate the easy magnetization direction. The results are in agreement with the distributed relaxation time theory.

A new metallic glass alloy characterized by high amplitude of magnetoelastic waves was synthesized. X-ray spectra evidenced the amorphous structure in the as-cast material, while differential thermal analysis confirmed the metastable initial phase and the occurrence of several crystallization peaks. The alloy shows a high difference between the glass transition and crystallization temperatures. Several heat treatments were performed and the structural relaxation effects were shown by means of the behavior of magnetization, Curie temperature and the resonant magneto-elastic wave amplitude. The strong increase of the last parameter, induced by the occurrence of the amorphous structure, is the most important result for application. Magnetic and magneto-elastic properties deteriorate if crystallization occurs, but in the optimal condition a partial nanocrystallisation may be present.