4. Summary

The magnetoresistance effect in a narrow strip of a suitably chosen NiFe alloy has much to offer for the detection of magnetic fields, and hence for reading out from magnetic tape or from a bubble memory. An approximately linear response can be obtained if the angle between the magnetization of the strip in the absence of a magnetic field and the direction of the measuring current is about 45°. Since the direction of the easy axis of magnetization is longitudinal and therefore coincides with the direction of the current, this is not possible without special precautions. In the solution described here, the 'barber pole', the strip is covered by oblique (45°) stripes of a relatively good conductor, and the current crosses 'at right angles' between the stripes. Except at very short wavelengths the MRH is much more sensitive than an inductive reading head, so that the amplifier noise plays a less important role. An MRH can be made very small and the principle allows special versions to be made for special applications, such as track-sensing heads and interference-suppressor heads. The technology is analogous to that required for thin-film circuits, but the temperature must remain below 400°C.