The fundamental principle of a spin valve is that the
resistance is dependent on the parallel or antiparallel
configurations of the two ferromagnetic electrodes, thus
associating the magnetoresistance (MR) effect, whose basic
structure consists of two ferromagnetic metals decoupled by the
insertion of a non-magnetic spacer. The MR effect in such a
sandwiched structure is the cornerstone of magnetic-sensing,
data-storage, and processing technologies, which is best
represented by the development of the giant magnetoresistance (GMR)
and tunneling magnetoresistance (TMR) information industry over the
past two decades.
