magnetoresistiviset

Magnetoresistiviset are devices and materials whose electrical resistance changes when exposed to a magnetic field. They are used to sense magnetic fields, determine position or current, and to store information in some memory technologies. The effect arises from spin-dependent electron transport in thin-film structures.

The most common realizations are giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), and anisotropic magnetoresistance (AMR). In GMR, the resistance depends on the relative alignment of ferromagnetic layers separated by a non-magnetic spacer. In TMR, electrons tunnel through a thin insulating barrier between magnetic layers, and the tunneling probability depends on magnetic alignment. AMR originates from spin-orbit coupling in a single ferromagnetic layer, producing resistance changes with the angle between current and magnetization.

Typical magnetoresistive devices are layered thin-film structures such as spin valves (for GMR) and magnetic tunnel junctions (for TMR). AMR devices usually involve bulk-like ferromagnets. Fabrication relies on sputtering or evaporation to produce nanometer-scale layers, sometimes capped with antiferromagnets to fix a reference magnetization.

Materials include ferromagnetic alloys such as nickel-iron (Permalloy) and cobalt-based compounds, non-magnetic spacers like copper, and tunnel barriers such as magnesium oxide. The magnetizations can be pinned with exchange bias to create a defined reference state.

Applications span hard-disk read heads, magnetic field sensors in automotive and industrial systems, current sensors, and magnetoresistive random-access memory (MRAM). The technology has driven significant improvements in sensitivity, speed, and power consumption.

The GMR effect was discovered in the late 1980s, leading to rapid adoption in data storage. TMR, demonstrated in the 1990s, further boosted performance and enabled MRAM. Today magnetoresistive devices are widespread in consumer electronics, automotive, and scientific instrumentation.