Magnetoresistive Sensors - Principles, Implementation and Applications,

The magnetoresistance effect was first observed in 1857. However, it only came into its own in the early 2000s following the discovery of giant magnetoresistance in 1988, leading to the Nobel Prize in Physics in 2007 for the main contributors to this discovery. In the late 1990s, the development of these devices accelerated, leading to their deployment in numerous industrial sectors. Since then, the popularity of these sensors has continued unabated. It has been driven by a number of factors: the excellent magnetic properties of these devices, their ease of manufacture and integration into existing technologies, and a steady improvement in their performance in line with industrial expectations.

The aim of this article is to provide an overview of the various existing technologies, their implementation, performance, target applications and current and future challenges. The main physical phenomena will be reviewed. They mainly exploit the quantum properties of electron spin. On the basis of these descriptions, a formalism based on the expression of resistance variation as a function of magnetic field will describe in academic terms how they are implemented. A focus on field-equivalent noise levels will be presented in order to give the best possible performance in terms of signal-to-noise ratio. The constraints associated with the construction of magnetometers, the only real tools enabling fine magnetic measurement in a few application examples, will also be discussed. Together, these elements will enable us to present major applications using these devices in a wide range of industrial fields. Today, these applications go far beyond their historical use as read heads for computer "hard disks", which marked the start of their industrial development.