Internal stress distribution in glass-covered amorphous magnetic wires

Abstract

During the preparation process of the glass-covered magnetic amorphous 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 ${\mathrm{Fe}}_{77.5}$ ${\mathrm{Si}}_{7.5}$ ${\mathrm{B}}_{15}$ glass-covered amorphous wires we found internal stresses of about ${10}^9$ 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 ${\mathit{M}}_{\mathit{r}}$/${\mathit{M}}_{\mathit{s}}$ (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 ${10}^8$ Pa.