The ever increasing demand for cheap logic and memory for bulk commodities will soon outrun scaling capabilities of flash type memories and CMOS technology in general.
For a suitable replacement one first needs to define the required features. For instance, an ideal (universal) memory should posses certain properties like high endurance, low power for writing and reading, fast switching and access, long retention times, etc. Hence, naturally new materials like ferroelectrics, magnetic semiconductors, and antiferromagnets will cause the introduction of new device structures and use the electron spin as an available degree of freedom.
Spin based devices and corresponding materials prove to be additionally beneficial due to the possibility of combining memory and logic in a single device, thus allowing true non-volatile information processing systems.
Many advantageous effects, specific to these spin based devises, have been found, e.g. spin-transfer torque, current induced domain wall motion, Tunnel MagnetoResistance (TMR), and Tunnel Anisotropic MagnetoResistance (TAMR).
Recently, a fully electrical read-write memory device out of a diluted ferromagnetic semiconductor (Ga,As)Mn has been demonstrated. It was considered to further extend the device's capabilities by connecting two such disks via a constriction. The overall electrical resistance of the structure is dominated by the resistance contribution of the constriction. Since the resistance of the constriction depends on the angle between its magnetization and current flow, this device can be facilitated to perform X(N)OR, (N)AND, and (N)OR logic operations. Although promising results have already been achieved, further research has to be carried out to overcome technological and physical obstacles as well as to gain more insight into this exciting research field.
The figure shows a possible current flow path for resetting the logic state of the structure.