Spintronics

Spintronics emerged from discoveries in the 1980s concerning spin-dependent electron transport phenomena in solid-state devices.

This includes the observation of spin-polarized electron injection from a ferromagnetic metal to a normal metal by Johnson and Silsbee (1985)[5] and the discovery of giant magnetoresistance independently by Albert Fert et al.[6] and Peter Grünberg et al.

Methods include putting a material in a large magnetic field (Zeeman effect), the exchange energy present in a ferromagnet or forcing the system out of equilibrium.

An important research area is devoted to extending this lifetime to technologically relevant timescales.

Two variants of GMR have been applied in devices: (1) current-in-plane (CIP), where the electric current flows parallel to the layers and (2) current-perpendicular-to-plane (CPP), where the electric current flows in a direction perpendicular to the layers.

[13] Spin-transfer, torque-based logic devices that use spins and magnets for information processing have been proposed.

[20] Two second-generation MRAM techniques are in development: thermal-assisted switching (TAS)[21] and spin-transfer torque (STT).

[24][25] Non-oxide ferromagnetic semiconductor sources (like manganese-doped gallium arsenide (Ga,Mn)As),[26] increase the interface resistance with a tunnel barrier,[27] or using hot-electron injection.

[33] Because external magnetic fields (and stray fields from magnetic contacts) can cause large Hall effects and magnetoresistance in semiconductors (which mimic spin-valve effects), the only conclusive evidence of spin transport in semiconductors is demonstration of spin precession and dephasing in a magnetic field non-collinear to the injected spin orientation, called the Hanle effect.

Applications using spin-polarized electrical injection have shown threshold current reduction and controllable circularly polarized coherent light output.

Future applications may include a spin-based transistor having advantages over MOSFET devices such as steeper sub-threshold slope.

Magnetic-tunnel transistor: The magnetic-tunnel transistor with a single base layer[35] has the following terminals: The magnetocurrent (MC) is given as: And the transfer ratio (TR) is MTT promises a highly spin-polarized electron source at room temperature.

In modern MRAM, detection and manipulation of ferromagnetic order by magnetic fields has largely been abandoned in favor of more efficient and scalable reading and writing by electrical current.