Internal stress distribution in glass-covered amorphous magnetic wires

Abstract

During the preparation process of the glass-covered magnetic aInorphous wires, axial, radial, and azimuthal internal stresses are induced, determining their magnetic properties. We have proposed a calculation method of the internal stresses induced during the solidification of the metal and during the cooling from the solidification temperature to room temperature due to the difference between the thermal expansion coefficients of metal and glass. For Fe77 QSi7 5B]5 glass-covered amorphous wires we found internal stresses of about 10 Pa. The values and distribution of these stresses depend on the radius of the metal and on the thickness of the glass cover. The stress distribution coupled with the specific high positive magnetostriction leads to an easy axes distribution associated with a magnetic domain structure consisting of a cylindrical inner core with axial magnetization and a cylindrical outer shell with radial magnetization.The inner core leads to the appearance of a large Barkhausen jump at low axial fields. We have calculated the ratio M"/M, (the reduced remanence) as being of about 0.75 -0.80. Magnetic measurements performed on samples prepared by us confirm the existence of the large Barkhausen jump but with a reduced remanence of about 0.95 that suggests the existence of a supplementary axial tensile stress. The dependence of the reduced remanence on external tensile stresses for wires covered by glass and after the glass removal confirms the existence of the supplementary stress whose value was estimated as being of the order of 10 Pa.

Rapidly Solidified Magnetic Nanowires and Submicron Wires

“…Therefore, at nanoscale, irrespective of composition, sample dimensions no longer allow the formation of a complex core-shell magnetic domain structure as a result of magnetoelastic energy minimization (Chiriac et al, 1995;Velázquez et al, 1996). Hence, despite the larger values of the internal stresses in these ultra-thin rapidly solidified materials, which coupled with the large positive magnetostriction of the Fe 77.5 Si 7.5 B 15 alloy lead to a large magnetoelastic term, the shape anisotropy is preponderant at nanoscale.…”

Engineering of giant magnetoimpedance effect of amorphous and nanocrystalline microwires

“…This method essentially consists of a simultaneous drawing of the composite microwire (metallic nucleus inside the glass capillary) through the quenching liquid (water or oil) jet onto rotating bobbins. More details on microwires preparation can be found elsewhere [5][6][7][8] We have measured the magnetic field dependence of impedance, Z, and GMI ratio, ΔZ/Z, for as-prepared samples and after heat treatments [5,6].…”

“…In the case of glass-coated microwires the main part of internal stress is induced by the glass coating during the simultaneous rapid solidification of metallic nucleus surrounded by glass coating during the glass-coated microwires preparation [6,8,18]. The strength of the internal stresses depends on the ρ-ratio between the metallic nucleus diameter, d, and total microwire diameter, D (ρ=d/D) [8,18] increasing with the the ρ -ratio decreasing. Therefore ρ -ratio is the other relevant parameter determining the magnetoelastic anisotropy.…”

“…A coercive field of both samples is about 4 A/m that is typical for amorphous Co-based glass-coated microwires with low negative magnetostriction constant. The origin of such magnetic softness is related to the internal stresses arising during preparation of glass-coated microwires [8,14]. These stresses give rise to an easy magnetization direction perpendicular to the wire axis, leading to an alignment of the magnetic moments in the direction which is perpendicular (circumferential) to the wire axis.…”

“…These properties are related to cylindrical symmetry as well as to crystalline structure of magnetic wires. On the other hand GMI effect and its magnetic field dependence are closely related to the internal and applied stresses [8][9][10]. Therefore both GMI and magnetic softness can be tailored by magnetic wires processing.…”