Abstract :
In the weird
world of quantum mechanics the fundamental, particle, electron possesses a
property Called ‘spin’. It is not the sort of spin used in common everyday
speech but, the angular momentum or the rotational momentum of a subatomic
particle that creates its own tiny magnetic field. By exploiting this spin
property, in a field called spintronics, computer scientists and physicists
have the potential to revolutionise the basis of computer processing and storage
technologies.
‘Spintronics’
can be a fairly new term for you but the concept isn’t so very exotic this technological
discipline aims to exploit the subtle and mind-bending esoteric quantum properties
of the electron to develop a new generation of electronic devices. The word
itself is a blend of electronics with spin, the quantum property it exploits.
Like so many words applied to the subatomic realm, you can refer spin
figuratively as a convenient label for a property that has no equivalent in
gross matter.
Every
electron exists in one of two states, namely, spin-up and spin-down, with its
spin either +1/2 or - 1/2 (refer Figs 1 and 2). In other words, an electron can
rotate either clockwise or anticlockwise around its own axis with constant
frequency. The two possible spin states naturally represent ‘0’ and ‘1’ states
in logical operations. And just because of this it is possible to make a
sandwich of gold atoms between two thin films of magnetic material that acts
as, a filter or a valve permitting only the electrons in one of the two states
to pass. The filter can be changed from one state to the other using a brief and
tiny burst of current.
There are
total three categories of spintronics based devices: 1) ferromagnetic metallic
alloy based devices, 2) semiconductor based devices and 3) the devices that
manipulate the quantum spin states of individual electrons for
information processing.
Ferromagnetic
metallic alloy based devices are mainly used in memory and information storage.
They are also termed as magnetoelectronics devices . They rely on the giant magnetoresistance (GMR) or
tunnelling magnetoresistance effect. Magnetic interaction is well understood in
this category of devices .
Semiconductor
spintronics devices combine advantages of semiconductor with the concept of
magnetoelectronics. This category of devices includes spin diodes, spin filter,
and spin FET. To make semiconductor based spintronic devices, researchers need
to address several following different problems. A first problem is creation of inhomogeneous
spin distribution. It is called spin-polarisation or spin injection.
Spin-polarised current is the primary requirement to make semiconductor
spintronics based devices. It is also very fragile state. Therefore, the second
problem is achieving transport of spin-polarised electrons maintaining their
spin-orientation. Final problem, related to application, is relaxation time.
This problem is even more important for the last category devices. Spin comes
to equilibrium by the phenomenon called spin relaxation. It is important to
create long relaxation time for effective spin manipulation, which will allow
additional spin degree of freedom to spintronics devices with the electron
charge. Utilizing spin degree of freedom alone or add it to mainstream
electronics will significantly improve the performance with higher
capabilities.
The third
category devices are being considered for building quantum computers. Quantum
information processing and quantum computation is the most ambitious goal of
spintronics research. The spins of electrons and nuclei are the perfect
candidates for quantum bits or qubits. Therefore, electron spin and nuclear
based hardwares are some of the main candidates being considered for quantum
computers.
Spintronics
based devices offers several advantages over conventional charge based
devices. Since magnetised materials
maintain their spin even without power, spintronics based devices could be the
basis of non-volatile memory device. Energy efficiency is another virtue of
these devices as spin can be manipulated by low-power external magnetic field.
Miniaturisation is also another advantage because spintronics can be coupled
with conventional semiconductor and optoelectronic devices.
However,
temperature is still a major bottleneck.
Practical application of spintronics needs room-temperature ferromagnet in
semiconductors. Making such materials represents a substantial challenge for
materials scientists.
From this simple
device it’s hoped to make incredibly tiny chips that will act as super-fast
memories whose contents will survive loss of power. The adjective is
spintronic. The ability to exploit spin in semiconductors promises new logic
devices. With enhanced fimctiona1ity higher speed, and reduced power consumption,
and might spark a revolution in the semiconductor industry. So far the problem
of injecting electrons with a controlled spin direction has held up the
realization of such spintronic devices.
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