V. Madurga

Modification of the saturation magnetostriction constant after thermal treatments for the Co58Fe5Ni10B16Si11 amorphous ribbon

Abstract A new method for measuring the magnetostriction constant has been developed. The resolution of this sensitive method allows to measure values of that constant as low as 10 -9 . It has been found that after thermal treatments, the magnetostriction constant of the amorphous ribbon whose nominal composition is Co 58 Fe 5 Ni 10 B 16 Si 11 changes not only its absolute value but also its sign. The kinetics of this variation has also been studied and a mean value of the activation energy of 0.8 eV for the relaxation process was obtained. Such variations of the magnetostriction constant are discussed as produced by modifications of the short-range order during annealing.

Experiments concerning the origin of stress anneal induced magnetic anisotropy in metallic glass ribbons

Abstract The stress anneal induced anisotropy has been studied in metallic glass ribbons of the compositions (Co 1- x Fe x ) 75 Si 15 B 10 , 0≤ x ≤0.12. The induced anisotropies are found to consist of two contributions, an irreversable one and a recoverable one. From their thermal variations and from their stress dependence the anisotropy constants have tentatively been related to the constituents of the saturation magnetostriction coefficients. The kinetics reveal for the recoverable anisotropy a continuous spectrum of activation energies in the range 1.55–1.8 eV.

Magnetic anisotropy in (Fe, Co)75Si15B10 and (Fe0.11Co0.89)72Mo3Si15B10 metallic glass ribbons, induced by constant stress and constant strain annealing

Abstract The magnetic anistropy induced by constant tensile stress and constant torsional strain annealing has been studied for liquid quenched alloys of the compositions (FexCo1−x)75Si15B10 (x = 0.1−1.0) and (Fe0.11Co0.89)72Mo3Si15B10. Within a certain annealing temperature range (depending on composition, pre-annealing time, applied stress and stress-annealing duration) the induced easy axis is perpendicular to the ribbon axis. After subsequent stress relief the easy axis turns parallel to the ribbon axis. The easy ribbon axis anisotropy produced in this way reveals a similar composition dependence as the anisotropy obtained by magnetic field annealing, but the anisotropy constant may be up to one order of magnitude larger, depending on the stress annealing conditions. In contrast to the field anneal induced anisotropy, the stress anneal induced anisotropy can be made permanent in the sense that it still remains after subsequent stress relief. It is furthermore shown that constant strain annealing induced anisotropy can be deduced from the properties observed after constant stress annealing, and a method for selecting proper stress relaxation conditions, with the purpose of obtaining maximum magnetic softness (isotropy) is proposed.

Different kinds of magnetic anisotropies induced by current annealing in metallic glasses

Abstract It has been previously shown that when flowing an electrical current along ribbon-shaped amorphous alloys, a transverse macroscopic magnetic anistropy was induced. In the present work, the modification of that induced anisotropy is investigated when the sample is additionally subjected either to external magnetic fields or to tensile stresses. Moreover, the kinetics of its activation process is analysed in the framework of a continuous spectrum of activation energies.

Short range order in (Fe, Co, Ni)75Si15B10 amorphous alloys determined from magnetic anisotropy

Abstract Some previously reported experimental results dealing with magnetostriction and induced magnetic anisotropy are analyzed with respect to the alloy composition. It is found that the properties which are affected by directional order vary with the composition as the probability for finding Bernal tetrahedral holes surround by 3Co1Fe or 3Fe1Co and not as the probability for finding metal—metal pairs as predicted by diatomic ordering theory for ideal solutions.

Influence of the anisotropy on the “SAMR” method for measuring magnetostriction in amorphous ribbons

Abstract The small angle magnetization rotation (SAMR) method has been found to be quite convinient for measuring magnetostriction in metallic glasses with low magnetostriction. Nevertheless the method fails in some sense when applied to high magnetostrictive samples. The origin of such failure has been analysed. The method becomes reliable when the sample saturates under the action of the axial field H z . On the other hand the sensitivity decreases with H 2 z . Since the internal str esses are the main source of anisotropy, via magnetoelastic coupling, the higher magnetostriction is, the stronger H z , required for saturating, becomes. Therefore the sensitivity of the method drops with the square of the magnetostriction of the sample. Some experiments confirming this explanation are shown.

Magnetostriction of amorphous (Co1−xFex)75Si15B10 ribbons (0 ⩽ x ⩽ 0.12) and its temperature dependence

Abstract Magnetostriction measurements as a function of temperature are reported for non-crystalline (Co 1− x Fe x ) 75 Si 15 B 10 ribbons with 0 ⩽ x ⩽ 0.12. The experimental results can be fitted with good overall agreement to phenomenological second-order polynomials in x and to the second and third power of the saturation magnetization. In the T room - T c range, magnetostriction compensation temperatures are observed for 0.04 ⩽ x ⩽ 0.05. The experimental results reported here clearly indicate that, when the Co matrix is perturbed with small amounts of Fe, the changes in λ s arise from different types of atomic interactions.

Anomalous eddy currents in magnetostrictive amorphous ferromagnets: A large contribution from magnetoelastic effects

Abstract An experimental arrangement has been used in order to rule out the contribution of domain walls to the magnetization process in Metglas 2605 Co and 2826 amorphous ribbons. The sample is placed in a longitudinal magnetic field while a tension is applied to ensure magnetic saturation. Then a current of frequency ω flows through the ribbon producing a small rotation of magnetization that appears as a variation of frequency 2 ω in the macroscopic longitudinal magnetization. Low frequency measurements confirm the role of rotations and allow the magnetostriction constant to be determined. At higher frequencies, magnetoelastic resonance peaks appear and the amplitude of magnetization variation drops about three decades below the prediction of eddy current theory, which has been developed for this particular case, both anomalous eddy currents from wall motion and magnetic aftereffects can be discarded so that a magnetoelastic mechanism is proposed to explain the observed behaviour.

Magnetostriction of the rapidly quenched Co80Nb8B12 alloy: dependence on quenching rate, structural relaxation, and temperature

Ribbons of nominal composition Co80Nb8B12 have been prepared by the single roller quenching method using different wheel velocities ranging from 26 to 42 ms−1. X‐ray diffraction patterns for ribbons prepared at low velocities show crystalline peaks but characteristic for the amorphous state for samples prepared at velocities above 36 ms−1. Room‐temperature values of the magnetostriction constant λs depend on the quenching rate and changes from 4×10−7 to −1×10−6 as the wheel speed increases. Zero magnetostriction samples are obtained at about 34 ms−1. Thermal treatments change the values of the magnetostriction in the same way as a decrease in the quenching rate does. A dependence of the magnetostriction constant on the applied stress has been found. This dependence, fully reversible, is observed at room temperature.

Relaxation processes and pure shear stress creep in a metallic glass ribbon of composition (Fe0.05Co0.95)75Si15B10

The effect of annealing time and temperature and of pre-annealing on the creep properties of metallic (Fe0.05Co0.95)75Si15B10 glass ribbons has been studied. The creep strains, measured in a torsional creep mode, can be well interpreted using the concept of an activation energy spectrum. Observed Int kinetics as well as deviations from this are comprehensible by considering the form of the characteristic annealing function.