Effect of magnetic field on the electrical properties:

As shown in Figure 27.03, the resistance is low when the magnetizations of all the ferromagnetic layers are parallel and the resistance becomes larger when the magnetizations of the neighboring ferromagnetic layers are ordered antiparallel.

Figure 27.03: Magnetic multilayers with (a) parallel and (b) antiparallel configurations.

GMR is defined as

where R_↑↑ and R_↑↓ are the resistance of the films under parallel and antiparallel configurations.