Tape wound cores are wound from soft magnetic alloy tape,

A disordered atomic structure without crystalline regions and grain boundaries is characteristic of amorphous alloys. This is a basic prerequisite that favors soft magnetic behavior.

From Spektrum der Wissenschaft 7 / 1994, page 108: "It is not at all easy to produce a metallic solid in which disorder prevails down to the smallest detail. While a melt solidifies during cooling, the metal atoms generally have enough time to form crystal nuclei, which grow locally into microcrystals. Only if the melt is cooled extremely quickly - for example, at one million degrees per second - does an amorphous solid form. As with glass, the atoms then remain in a largely disordered state. …

Solidification in fractions of a second … To achieve cooling rates of one million degrees per second, however, its thickness must be well below 0.1 millimeters. This is essentially controlled by the roll speed: 0.02 to 0.04 millimeters can be achieved at 20 to 50 meters per second. The dimensions of the casting nozzle and the chill roll determine the film width.

Soft against changing magnetic fields … This is most noticeable when the magnetic field direction changes again. In a metal with a lattice structure, it often takes more energy to restore the original state. Initially, a residual magnetization remains, which is called remanence. An additional field force - the coercivity - is required to bring the magnetic moments back to their original state. For applications in alternating fields, soft magnetic materials that remagnetize even in weak fields are therefore preferred. These include amorphous metals and nickel-iron alloys. …" Soft magnetic iron-amorphous strips, produced using rapid solidification technology, are used for the production of amorphous cut and toroidal strip cores.Cut strip cores