magnetoresistanssieffektien

Magnetoresistance effects describe changes in the electrical resistance of a material when it is exposed to a magnetic field. The phenomena span a range of mechanisms and magnitudes, from small classical responses to large, technologically important changes in resistance.

Various mechanisms contribute to magnetoresistance. Ordinary magnetoresistance arises from the Lorentz force acting on moving charge carriers, which alters their trajectories and scattering, typically giving a modest increase in resistance that grows with the magnetic field. In ferromagnetic materials, anisotropic magnetoresistance depends on the angle between the current and the magnetization due to spin‑orbit coupling. More pronounced effects occur in multilayer structures and junctions: giant magnetoresistance results from spin-dependent scattering in alternating ferromagnetic and nonmagnetic layers, producing large resistance changes when the relative magnetic alignment switches from parallel to antiparallel. Tunnel magnetoresistance occurs in magnetic tunnel junctions, where electrons tunnel through an insulating barrier between ferromagnetic electrodes and the tunneling probability depends on the relative magnetization, yielding very large resistance changes. Colossal magnetoresistance is observed in some manganites and related oxides, where complex interactions between charge, spin, and lattice lead to substantial resistance changes in modest magnetic fields.

In addition to these, quantum corrections to conduction at low temperatures can produce magnetoresistance through phenomena such as weak localization and universal conductance fluctuations, contributing to the diversity of observed behaviors.

Historically, magnetoresistance has been studied since the 19th century, with the discovery of basic effects and the later identification of GMR in 1988 by Albert Fert and Peter Grünberg, which earned the Nobel Prize in Physics in 2007. Today, magnetoresistance effects underpin many technologies, including read heads for hard disks, magnetic random-access memory, and a broad range of magnetic-field sensors.