Spin valve

Due to the difference in coercivity, the soft layer changes polarity at lower applied magnetic field strength than the hard one.

The invention of spin valves is credited to Dr. Stuart Parkin[1] and his team at IBM Almaden Research Centre.

Dr. Parkin is now serving as the Managing Director of the Max Planck Institute of Microstructure Physics in Halle, Germany.

Due to a split in the density of states of electrons at the Fermi energy in ferromagnets, there is a net spin polarisation.

Thus if both the fixed and free layers are polarised in the same direction, the device has relatively low electrical resistance, whereas if the applied magnetic field is reversed and the free layer's polarity also reverses, then the device has a higher resistance due to the extra energy required for spin flip scattering.

A schematic diagram of a pseudo spin valve. The free layer is magnetically soft and the fixed layer is magnetically hard. When the magnetic layers are antiparallel the electrical resistance is higher than when they are aligned.