Spintronics

IBM-Stanford Spintronic Science and Applications Center

What is spintronics?
The word "spintronics" (short for "spin electronics") refers to devices
that take advantage of electrons' quantum property called "spin." Electrons
don't actually spin around an axis, although in many ways they may behave as
if they do. More familiar is the electron's quantum property of "negative
charge": Moving charge creates electrical current.

Electron spin has two possible states, either "up" or "down." Aligning spins
in a material creates magnetism. Moreover, magnetic fields affect the
passage of "up" and "down" electrons differently. Under normal conditions,
the spins of conducting electrons are roughly half-up and half-down.
Controlling the spin of electrons within a device can produce surprising and
substantial changes in its properties. A new generation of devices based
upon the manipulation of spins in solids may have entirely new functionality
that could provide a foundation for entirely new computational paradigms.

For example, the first widely used spintronic device -- the Giant
Magnetoresistive (GMR) spin-valve head for magnetic hard-disk drives --
exhibits large changes in electrical resistance due to variations in the
relative magnetic orientation of layers on either side of a spacer layer
only 2-3 atoms thick. When the orientations are in the same direction
("parallel"), electrons with one type of spin pass freely while those with
the opposite spin meet greater resistance. When the magnetic orientations
are in opposite directions ("antiparallel"), all the electrons meet
resistance, resulting in a high overall electrical resistance through the
head. By designing the structure so a faint external magnetic field would
change the relative magnetic orientations of the key layers, the GMR head
became an extraordinarily sensitive magnetic-field sensor. Pioneered by IBM
in 1997, the GMR head enabled hard-disk drives to read smaller data bits,
which led to a more than 40-fold increase in data-storage density over the
past seven years.

Spintronic structures are also at the heart of Magnetic Random Access Memory
(MRAM), a fast non-volatile memory concept originally proposed by IBM and
currently being developed by IBM, Infineon and others.

 

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