J. Carrizo

Induced magnetic anisotropy in amorphous ribbons by applying a magnetic field during the quenching process

A method to induce magnetic anisotropy in amorphous magnetic ribbons has been developed. The anisotropy is induced in the high Curie temperature Fe80B20 and Co70Mn5Fe1Mo1Si14B9 amorphous magnetic ribbons by applying a magnetic field at the moment of the solidification of the melt. This method does not affect the excellent mechanical properties of these materials. The induced magnetic anisotropy has been measured by torque magnetometry and its strength and easy axis are compared with the results obtained by other authors using static magnetic annealing in similar samples.

Mechanical determination of internal stresses in as-quenched magnetic amorphous metallic ribbons

The layer removing method for determining the internal stress distribution through thickness in sheets has been applied to metallic glass ribbons. The internal stresses are obtained from the variation of the radius of curvature of the samples when the layers are removed. The experimental technique used is described here and the results for two ribbons, are presented. A general feature has been observed implying compressive stress near both surfaces (a strong one near the drum surface and a weak one near the air surface), and the central part under tensile stress. This is in agreement with the residual stress distribution shown by other materials after fast cooling procedures.

Influence of thickness and roughness on the anisotropy of asquenched Co-based amorphous magnetic ribbons

Abstract The magnetic anisotropy of two near-zero-magnetostriction Co-based amorphous ribbons with high and low Curie temperatures was measured by torque magnetometry in samples with different thicknesses. It was found that the thicker ribbons have a lower anisotropy in samples with low T c , whilst in those with high T c the result is inverted, the thicker ones having a larger anisotropy, always along the ribbon axis. This behavior can be interpreted in samples with high T c as being due to an induced anisotropy produced by the alignment of the magnetization along the ribbon axis by the shape effect during the quench. This interpretation would also account for the increase of anisotropy with annealing in these kinds of samples. For lower T c , the induced anisotropy diminishes and the surface roughness anisotropy plays a more important role. Mechanical polishing confirms this assumption.

Evaluation of anisotropy torque measurements in magnetic amorphous ribbons

Abstract Torque curves of several Fe- and Co-based amorphous ribbons have been obtained by torque magnetometry. Large increases in the value of the uniaxial anisotropy constant K u derived from the torque curves for each alloy has been observed in a range of applied fields for which the samples are practically saturated. This result is interpreted as being due to the contribution to the torque of unsaturated imperfections in the samples that occupy a small volume but can exhibit high anisotropy. Estimates of the volume fractions and anisotropies are made.

Stress relief and magnetic properties of magnetostrictive Fe79B16Si5 amorphous magnetic ribbons

Abstract The in-plane magnetic anisotropy constant and surface magnetization curves have been measured for magnetostrictive Fe 79 B 16 Si 5 amorphous ribbon in the as-quenched state and after two isothermal annealing treatments. The variation of the residual stress distribution with the thermal treatments has been obtained and related to the changes in the magnetic properties. The results obtained show that the residual stresses are the main source of the in-plane magnetic anisotropy, they act as pinning centers for the wall displacements, and they are mainly near the surface.

Analysis of the in-plane magnetic anisotropy in amorphous ribbons obtained by torque magnetometry

The evolutions of the uniaxial torque and magnetization with the applied magnetic field allow us to discriminate the sources of in-plane magnetic anisotropy in amorphous ribbons. In order to determine the magnetic anisotropy sources, a simple model has been developed for an inhomogeneous material. We apply this model to explain the quite different behavior observed in the evolution of the uniaxial torque amplitude with the applied magnetic field of two commercial Co-based amorphous alloys.

Anisotropy and roughness in as-quenched Co66Si16B12Fe4Mo2 amorphous ribbons

Abstract The magnetic anisotropies of several disc-shaped samples of as-quenched Co 66 Si 16 B 12 Fe 4 Mo 2 have been measured by torque magnetometry. The samples were polished on both sides mechanically and electrolytically in order to study the influence of roughness on the anisotropy of this kind of samples of low magnetostriction and low Curie temperature. The results from torque magnetometry show that after mechanical polishing the anisotropy of the sample practically vanishes, while in the case of electrolytic polishing the measured anisotropy increases. We can conclude that the only detectable anisotropy in these samples originates in the presence of oriented surface roughness. In the case of electrolytic polishing the mean anisotropy of the sample increases because the roughness is hardly altered, while the sample volume is considerably reduced.

Analysis of the magnetic anisotropy induced by applying a magnetic field during the quenching process in amorphous ribbons

The magnetic anisotropy induced in amorphous magnetic ribbons by applying a magnetic field to the melt during the solidification process is analyzed. Using a model based on the magnetization curve and on the evolution of the uniaxial torque with the applied magnetic field, the volume fractions of the sample affected by the different magnetic anisotropies are obtained for the ribbons of composition Fe80B20 and Co70Mn5Fe1Mo1Si14B9. The results are compared with those obtained in the ribbons of the same composition but with anisotropies induced by the static magnetic annealing. From these results, the different sources of the field-quenching-induced magnetic anisotropy in those amorphous magnetic ribbons are analyzed.

Structural relaxation and viscosity in Co-based amorphous materials

Abstract The variation of viscosity of Co 69 B 12 Si 12 Fe 4 Mo 2 Ni 1 and Co 70 Si 14 B 9 Mn 5 Fe 1 Mo 1 amorphous materials with isothermal and isochronal annealing has been obtained. The results show that there is an increase of the viscosity as the temperature and the time of the thermal annealing increase. This behaviour is explained as a consequence of the structural relaxation of these materials due to their metastable condition in the as-quenched state. The annealing process produces changes in the topological short range order and in the chemical short range order.

Torque measurements in low-magnetostriction Co70(Si + B)23Mn5(Fe + Mo)2 amorphous ribbons

Abstract Torque measurements have been made on circular samples of Co 70 (Si + B) 23 Mn 5 (Fe + Mo) 2 of low magnetostriction and medium Curie temperature (350°C). The samples were measured as-quenched and after mechanical polishing and annealing. Careful mechanical polishing reduces the measured magnetic anisotropy by half, and further annealing removes it completely. Magnetic annealing restores an anisotropy of the order of the value previously measured. The results and the origin of the anistropy in this kind of sample are discussed.