There are various methods with which the resistance value of conductive materials can be influenced under the influence of a magnetic field. These effects, which are grouped under the generic term X-Magneto-Resistive(XMR), are implemented in magnetic field sensors and magnetometers.
Anisotropic Magneto-Resistive( AMR) uses the effect that the resistance value of magnetically highly permeable metal alloys changes due to the direction of the magnetic field. These alloys, such as permalloy or mu-metal, have a material structure in which the electrical resistance is directional, or anisotropic.
When a magnetic field is applied to the meandering alloy, its resistance value changes depending on the angle between the magnetization and the direction vector of the resistance. If the material is operated in magnetic saturation, the resistance change depends solely on the orientation of the material structure in relation to the magnetization angle. The resistance value changes with the square of the magnetic field strength. A magnetic field sensor based on the AMR effect is thus ideal for measuring changes in angle. The AMR effect also works at high frequencies up into the gigahertz range.
AMR magnetic field sensors consist of a very thin permalloy layer with ferromagnetic properties and thin metal strips that serve to correct for nonlinearities. There are two perpendicular directions of magnetization, one of which leads to the change in resistance when rotated.
In addition to the AMR effect, there are other magneto-resistive effects, such as Giant Magneto-Resistive( GMR), which is used to increase the storage density ofhard disks, Colossal Magneto-Resistive ( CMR), Tunneling Magneto-Resistive( TMR) and Extraordinary Magneto-Resistive( EMR).