Magnetresistans

Magnetresistans, or magnetoresistance, refers to the change in a material’s electrical resistance when it is exposed to a magnetic field. The term covers several distinct effects, from small changes in ordinary metals to large, technologically important changes in specialized structures.

Ordinary magnetoresistance (OMR) arises from the Lorentz force acting on moving charge carriers, which alters their trajectories and reduces conductivity. In most bulk metals at practical field strengths, this effect is modest.

Anisotropic magnetoresistance (AMR) occurs in ferromagnetic materials, where resistance depends on the angle between the current and the magnetization due to spin-dependent scattering in the crystal lattice.

Giant magnetoresistance (GMR) was discovered in multilayer thin films of alternating ferromagnetic and nonmagnetic metals. The electrical resistance is much higher when the magnetic moments of the ferromagnetic layers are antiparallel than when they are parallel. GMR was unveiled independently by Fert and Grünberg in 1988 and helped launch modern spintronics; it underpins sensitive read heads for hard-disk drives.

Colossal magnetoresistance (CMR) describes large resistance changes in certain manganese oxides at modest magnetic fields, linked to strong electron correlations and phase competition.

Tunneling magnetoresistance (TMR) occurs in magnetic tunnel junctions, where two ferromagnetic electrodes are separated by an insulating barrier. The tunneling probability depends on spin alignment, producing large magnetoresistance ratios used in read sensors and emerging memory applications (MRAM).

Applications span data storage, magnetic sensing, and spintronic devices. Materials include conventional ferromagnets for AMR and GMR, oxide manganites for CMR, and engineered ferromagnet–insulator systems for TMR.