Spin valves and their application

Abstract

The discovery of giant magnetoresistance (GMR) in the late 1980's resulted in massive interest in the deposition and characterisation of artificial layered magnetic structures. Spin valves were discovered in 1991 and have been the subject of intense interest due to their suitability for application in magnetoresistive read heads in magnetic hard disk drives. The basic element of a spin valve is two ferromagnetic layers separated by a non-magnetic spacer. The electrical resistance of the structure is low when the magnetisation directions of the ferromagnetic layers are aligned parallel and high when they are antiparallel. One of the ferromagnetic layers, the free layer, switches magnetisation direction close to zero field. The other layer, the pinned layer, is grown next to an antiferromagnet and its magnetisation direction is pinned at low fields. Switching of the free layer at low fields, therefore, results in a transition from the parallel to antiparallel state and a linear change in resistance. Hence the spin valve is a highly sensitive magnetic field sensor and can be used in several applications. Spin valves can also be considered as one of the fundamental building blocks necessary for developing more complicated spin electronic devices.