SPINTRONICS-FUTURE OF ELECTRONICS.
ABSTRACT
Spintronics also called as magnetoelectroincs deals with the use of spin of electrons rather than the charge of electrons to store, process and data signal. There are many announcements to make drive of 1 TB on single sided 3.5" diameter disc using spintronics. There are various techniques involved that use semiconductor as well as metal for exploiting spin. MRAM is the most acclaimed product of spintronics, it uses magnetic tunnel concept in working and is non-volatile and more robust. One of the major advantages of spintronics over electronics is that magnets tend to stay magnetized, which is sparking in the industry an interest for replacing computer' semiconductor based components with magnetic ones, starting with the RAM.
WHAT IS 'SPINTRONICS'?
Spintronics or spin electronics refers to the study of the role played by electron(and more generally nuclear) spin in solid state physics and possible devices that specifically exploit spin properties instead of or in addition to the charge degree of the freedom. By exploiting this spin property, the basis of computer processing and storage technologies has been revolutionized. The word 'spintronics' itself is a blend of electronics with spin, which is the angular or rotational momentum of a subatomic particle that creates its own tiny magnetic fields. The ability to exploit spin in semiconductors promises new logic devices with enhanced functionality, high speed and reduced power consumption.
PRINCIPLE INVOLVED
Spintronics is based on the spin of the electron rather than its charge. Every electron exists in one of the two states, namely, spin-up and spin-down, with spins either positive half or negative half. Spin is the root cause of magnetism and is a kind of intrinsic angular momentum that a particle can not gain or lose. The two possible spin states naturally represent '0' and '1' in logical operations, so it i possible to make a sandwitch of gold atoms between two thin films of magnetic material that ll act 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 another using a brief and tiny burst of current. Spin is the characteristics that makes the electron a tiny magnet, compete with north and south poles. The orientation of the tiny magnet's north-south axis depends on the particle's axes of spin. In the atoms of an ordinary material, some of these spin axes point up(with respect to say, an ambient magnetic field) and an equal number points 'down'. The particle's spin is associated with a magnetic moment, which may be thought of as the handle that lets a magnetic field torque the electon's axis of spin. Thus in ordinary material, the up moments cancel the down ones, so no surplus moment piles up.
For that a ferromagnetic like iron, nickel or cobalt is needed. These have tiny regions called 'domains' in which an excess of electrons have spins with axes pointing either up or down-atleast, until heat destroys their magnetism, above the metal's Curie temperature. The many domains in the direction of the field, so they point in the same direction. The result is a permanent magnet.
WORKING
When a pool of spin-polarized electron is put in a magnetic field, precession occurs. The frequency and the direction of rotation depend on the strength of the magnetic material in which precession is taking place. Thus if a voltage pushes an electron out of gallium arsenide into zinc selenide the electrons precession characteristics changes. However, if a higher voltage pushes the electron sharp enough into zinc selenide, the precession characteristics do not change but remain those of gallium arenide for a while. n-type materials rely on electrons, while p-types on poles to carry current. Because the materials are of two different charge carrier types, an electric field is formed around their junction. This field is strong enough to pull a poll of spin coherent electrons from GaAs immediately into ZnSe where coherence persists for hundreds of nanoseconds. Now, n-type and p-type materials can be built and the spin can get through the interface between them just fine. The spin can be moved from one kind of semiconductor into another without the need of any extenal field. Basically all spintronics devices act according to the simple scheme: the information is stored(written) into spin as a particular spin orientations(up or down). The spins, being attached to mobile electrons, carry the information along a wire and the information is read at a terminal.
