INTERNAL-STRESS DISTRIBUTION IN GLASS-COVERED AMORPHOUS MAGNETIC WIRES

During the preparation process of the glass-covered magnetic amorphous wires, axial, radial, and azimuthal internal stresses are induced, de termining their magnetic properties. We have proposed a calculation me thod of the internal stresses induced during the solidification of the metal and during the cooling from the solidification temperature to r oom temperature due to the difference between the thermal expansion co efficients of metal and glass. For Fe77.5Si7.5B15 glass-covered amorph ous 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 w ith 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 o uter shell with radial magnetization. The inner core leads to the appe arance of a large Barkhausen jump at low axial fields. We have calcula ted the ratio M(r)/M(s) (the reduced remanence) as being of about 0.75 -0.80. Magnetic measurements performed on samples prepared by us confi rm the existence of the large Barkhausen jump but with a reduced reman ence of about 0.95 that suggests the existence of a supplementary axia l tensile stress. The dependence of the reduced remanence on external tensile stresses for wires covered by glass and after the glass remova l confirms the existence of the supplementary stress whose value was e stimated as being of the order of 10(8) Pa.