1. Foreword

Ir W. J. van Gestel and Dr F. W. Gorter are with Philips Research Laboratories, Eindhoven; Ir K. E. Kuijk, formerly with Philips Research Laboratories, is now teaching at the Hogere Technische School, Eindhoven.

The discovery of a new physical effect or a new property of a material is often completely unrelated to its technical exploitation. A clear example of this is the magnetoresistance effect, which can occur in alloys that are ferromagnetic. In this effect the magnitude of the electrical resistivity depends on the angle between the direction of the current and the ferromagnetic magnetization. It was discovered in both nickel and iron in 1857, but it is only in the last few years that there has been any recognition of its significance in magnetic recording.