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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.

The effects of heat treatments in vacuum on magnetic permeability, Young's modulus and magnetoelastic wave amplitude were investigated in the amorphous ferromagnetic alloys Fe73.5Cu1Ta3Si15.5B7 and Fe73.5Cu1W3Si15.5B7 where tantalum or tungsten replaces niobium, which mas generally used with the same atomic fractions of the other elements. The stress sensitivity coefficient was also theoretically deduced in its development vs. the applied magnetic bias field. Structural relaxation and crystallization consequences are evidenced. Moreover an already predicted relation between the maximum of magnetoelastic wave amplitude and the minimum of stress sensitivity coefficient was confirmed.

The role of magnetoelastic energy to determine the causes which affect the magnetic anisotropy are reviewed. The simple model used to describe magnetostriction in the new nanostructured materials is reported. Starting from this model the magnetostriction in multilayer samples, of the kind magnetic material/non-magnetic material, is discussed. In particular the fundamental influence of the interlayers is shown. Finally it is demonstrated that by measurement of saturation magnetostriction it is possible to have information on the interlayers thickness and average composition.

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

Interaction between acoustic field and electromagnetic field, in a magnetostrictive ferromagnetic material produces both transversal quasiacoustic waves (QACW) and quasielectromagnetic waves (QEMW) named hybrid waves. Properties of hybrid waves have been studied and their dependence on conductivity has been emphasized in the piezomagnetic case. To this end, the system of Maxwell’s equations, Newton’s law of force, and piezomagnetic state equations were solved for an infinite continuous medium. It is shown that for a particular conductivity value σc, the hybrid modes coincides in a mixed propagation mode we called MHWM. The dispersion relation, in the case of separate hybrid waves, as well as in the mixed mode MHWM, is discussed. The MHWM has a velocity Vc, which is independent of wave number k. Moreover we point out that (a) for very high σ, the QEMW velocity reaches a k‐independent value while the QACW velocity falls to zero, (b) the behavior of σc(k), at constant Vc, is linear, (c) for σ≠σc, at constant...

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.

A contribution to the investigation of the stress effect on the saturation magnetostriction of polyerystalline rods stressed by torsion is presented. The critical torsional stress above which magnetostriction remains constant is found and the crystal anisotropy level, at various torsions, is estimated. As in the tensional case, the effect of crystal anisotropy at the critical stress has not been clearly interpreted so far. A study of the behaviour of the magnetization curve near saturation provides a possible explanation.

Magnetoelastic wave amplitude, a, was measured vs. the temperature during thermal cycles in Metglas 2826. When the Curie temperature, T C, has been reached, the A value vanishes due to the fall of the magnetoelastic coupling in the paramagnetic state. This allows evaluation of the T c temperature. The latter increases after the iterated thermal treatments while the magnetic anisotropy K u decreases. Also the A amplitude, measured at room temperature after the subsequent thermal treatments, shows an increasing behaviour. The values of K u, T c and A approach saturation after the same number of thermal cycles; this suggests that the structural relaxation produced by annealing is the microscopic mechanism governing all the three physical quantities. In particular we explain the connection between K u and A by means of the longitudinal magnetostriction.

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

C.w. laser annealing of metglas 2826 ribbons was performed by varying beam power and irradiation time. A simplified thermal model was elaborated to have information about the temperature rise of the samples and the occurrence of crystallization. The predictions were in agreement with the experimental results. The laser-induced changes of magnetic and mechanical properties were particularly tested by means of the magnetostrictive response and the Young-modulus variations.

The anisotropy induced by magnetic annealing in a transversal field is correlated with the Young modulus, the longitudinal magnetostriction and the magnetoelastic coupling coefficient. Subsequently it is shown that the value of the anisotropy deriving from directional short-range ordering,kDSRO, can be calculated in an original manner by means of the mentioned parameters. ThiskDSRO evaluation is in increasing agreement with its directly measured value, when the magnetic-annealing effects approach saturation. The magnetic heat treatment influences can be described by a small rise of the internal stress, in comparison with conventional annealing, and a large increase of longitudinal magnetostriction.

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 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.