Spinvalves

Spinvalves are multilayer thin-film devices that exploit the giant magnetoresistance (GMR) effect to produce a change in electrical resistance based on the relative orientation of magnetizations in adjacent ferromagnetic layers. A typical spin valve consists of two ferromagnetic layers separated by a non-magnetic spacer; one ferromagnetic layer acts as a pinned reference layer, whose magnetization is fixed by exchange bias with an adjacent antiferromagnetic material, while the other is a free layer whose magnetization can rotate under external magnetic fields or spin-transfer torques.

The spacer is commonly a metal such as copper. When the magnetizations of the two ferromagnetic layers are parallel, spin-dependent scattering yields a lower resistance; when they are antiparallel, scattering increases and resistance rises. The magnitude of the resistance change—the GMR effect—depends on the materials, layer thicknesses, and interface quality and can be substantial in optimized structures.

Spinvalves have become fundamental components in magnetic sensing and read-out technologies. They are widely used as magnetic sensors in read heads for hard disk drives and in various spintronic devices that require sensitive, reversible resistance changes. They also appear in research and development for spin-transfer torque applications and certain magnetic memory concepts, though practical MRAM devices often use magnetic tunnel junctions (MTJs) with tunnel magnetoresistance (TMR).

Historically, spinvalves were discovered independently by Albert Fert and Peter Grünberg in 1988, a breakthrough that earned the Nobel Prize in Physics in 2007. The term distinguishes devices with metallic spacers and GMR from MTJ-based structures that rely on insulating barriers and TMR.