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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.

Multilayered amorphous ribbons were produced by electrolytical deposition. They have exceptional magnetoelastic properties which enhance the amplitude of longitudinal magnetoacoustic waves travelling in the samples, also in comparison with similar-size ribbons of conventional metallic glass obtained by rapid quenching from the melt.

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.

Elasticity moduli at constant magnetic field and at constant induction as the functions of magnetic bias field of the strips of Fe/sub 20/B/sub 12/Si/sub 8/ metallic glass annealed in vacuum at temperatures of 370 and 380/spl deg/C were investigated. The values of moduli in as-quenched state were changing from 133 to 155 GPa. After annealing at 370/spl deg/C the moduli changes were from 80 to 170 GPa and after heat treatment at 380/spl deg/C /spl Delta/E effect increased and these changes were from 60 to 170 GPa. >

Experimental evidence of magneto-elastic wave amplitude enhancement by thermo-elastic waves is reported. This enhancement is shown to be optimized under resonance conditions. The thermo-elastic waves have been excited in a metal alloy ribbon sample by a high repetition rate CO 2 laser. The results are explained in terms of a simple theoretical treatment of the thermo-magnetic elastic waves under the conditions investigated.

The piezomagnetic coupling coefficient (the <>) is quantitatively investigated below room temperature and a comparison is made among polycrystalline samples and amorphous ones. The technique used is an original one. It experimentally consists in the measurement of the amplitude of magnetoelastic waves, their resonance frequency and differential susceptibility; theoretically, it consists in coupling Newton's law of force with the piezomagnetic state equations. The results clearly show different responses of polycrystalline samples with respect to the amorphous ones; in particular the nonmonotonic behaviour of the <> for metallic glasses is interesting for establishing their actual magnetic states at low temperature.

The actual knowledge on Co-P electrodeposited alloy is reviewed. The differences among the experimental conditions of production, and their influnce on the obtained material as well, are discussed. Recent results both in microcrystalline layers and in amorphous multilayers are reported. In particular the attainment of not-trivial magnetoelastic properties is emphasized.

The thermal model describing the c.w.-annealing of ribbon-shaped materials irradiated by a moving laser beam has been revised and imrpoved. New experimental results on the initial permeability of annealed metallic glasses are presented. © 1983 Società Italiana di Fisica.

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 theory of the experimental apparatus used for producing and revealing magnetomechanical waves, was elaborated. It was demonstrated that, in the investigated case, the measured amplitude of the elastomagnetic waves is a function of the reversible permeability as well as the elastic and piezomagnetic coefficients. All the last parameters are sensitive to both structure changes and magnetic interaction variations. Therefore during the heat treatment the magnetoelastic wave amplitude is a physical sensor with which we can investigate phase transitions. On this basis the effects of the structural relaxation, the ferro-paramagnetic state transition and the amorphous-crystalline structure development, were investigated in samples of metallic glass.

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.