Magnetoresistance is the phenomenon where the electrical resistance of a material changes in the presence of a magnetic field. In other words, it is a change in the electrical resistance of a material due to the application of an external magnetic field.
There are two types of magnetoresistance: positive magnetoresistance and negative magnetoresistance. In positive magnetoresistance, the electrical resistance of the material increases when a magnetic field is applied, while in negative magnetoresistance, the resistance decreases.
Magnetoresistance is used in a variety of applications, including magnetic sensors, magnetic random access memory (MRAM) devices, and in the study of the electronic properties of materials. The effect is particularly important in materials with low electrical resistance, such as metals and semiconductors, and can be used to measure the strength of a magnetic field.