J.M. González

Induced magnetic anisotropy and change of the magnetostriction by current annealing in Co-based amorphous alloys

Abstract Magnetic anisotropies can be induced in amorphous alloys by different treatments such as cold rolling and stress or field anneal. In this work, we present the experimental results concerning the magnetic anisotropy induced by transverse field annealing. Here, the magnetic field has been created by an electrical current flowing along the amorphous ribbon. This current produces simultaneously an increase of the temperature of the sample and the field necessary to induce the transverse anisotropy. This method is convenient due to the rapidity in obtaining the equilibrium annealing temperature and the simplification of the experimental set-up. However inhomogeneity in both annealing temperature and applied field cannot be avoided. The kinetics exhibit a similar behaviour to that observed by using the conventional magnetic annealing method. Correlated changes of the magnetostriction are also presented. It is to be noted that these changes do not affect the compensation temperature. These investigations have been carried out for two Co-based amorphous alloys whose nominal compositions are (Co0.95Fe0.05)75Si10B15 and (Co0.92Fe0.08)75Si15B10.

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.

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.

Effects of current annealing on the hysteresis loop of amorphous alloys

As has been previously reported, an electrical current flowing along ribbon-shaped metallic glasses can induce a desired magnetic anisotropy (current-annealing technique). In the present work the modification of the hysteresis loop parameters of two Co-rich amorphous alloys by current annealing has been investigated. In addition, the inhomogeneity of the induced magnetic anisotropy has been evaluated from the tensile stress dependence of the coercive fields of the samples.

Helical anisotropy induced by annealing in metglas 2826

Abstract The magnetic anistropy induced by constant torsional strain annealing of an amorphous alloy with nominal composition Fe 40 Ni 40 P 14 B 6 has been studied. The influence of annealing conditions is reported and discussed. The experimental results indicate that magnetoelastic coupling is the main source of the induced anisotropy, the anelastic and plastic creep contributions being almost negligible.

Determination of internal stresses distribution for a nearly-zero magnetostriction amorphous alloy

Abstract Surface and bulk magnetization curves have been measured by means of the magneto-optic Kerr effect and the conventional induction method, respectively, for the Metglas 2705 M alloy. From the analysis of the experimental measurements and using a simplified model, the angular and intensity distributions of the internal stresses have been evaluated.

Crossover from local to collective magnetic relaxation modes in Co/Ni multilayers

We study the time dependence of the magnetization at constant applied field in Co/Ni multilayers. Our results evidence that, depending on the magnitude of the measuring field, it is possible to observe either local thermally activated magnetization reversal processes (fields significantly lower than the coercive force) or collective relaxation modes (fields linked to large differential susceptibility values, non-repetitive stair-like decays).

Magnetization reversal and anisotropy in CoO/permalloy/Cu/permalloy/NiO layered structures

This work presents results on the temperature dependence of the hysteretic processes of glass /CoO/permalloy/Cu/permalloy/NiO layered structures. The antiferromagnetic behavior of both oxides below their different blocking temperatures leads to the apparition of unidirectional anisotropy and enhancement of coercivity in the permalloy layers. The magnetization reversal is influenced by the exchange coupling between the permalloy layers, which is controlled by the Cu thickness. Both ferromagnetic layers remain uncoupled for 7.5 nm Cu thickness and are coupled for 1.5 nm. The hysteresis loops measured along different directions of the samples at room temperature point out the different features in the magnetization processes of systems with uniaxial and/or unidirectional anisotropies.

Torsional elastic behaviour in Metglass Fe40Ni40P14B6

Measurements of torsional stress as a function of strain were carried out in as-quenched and cold-rolled amorphous ribbons of Metglass 2826, at room temperature and 77K. These samples show a giant reversible, but nonlinear, region of about 60 pi rad m-1. The observed behaviour seems to be a consequence of a freezing-in plastic flow mechanism, for room and lower temperatures, which increases the reversible region beyond the linear limit, and therefore higher order products of strains in the free energy development are needed.