“Spin Transport electronics” is real(full) name for Spintronics. In Spintronics we mainly focus on spin and magnetic moment of the electron rather than electronic charge which we count in solid state studies. There are two types of spin : Up spin and Down spin ( In real Clockwise and Anti-Clockwise ). Key concept of Spintronics is to control the spin of electron and use it in our favour.
Spintronics has many applications. One of them is fast and efficient data storage. MRAM (Magnetic Random Access Memory) is based on spintronics. It is fast,small in size and Stable than other storage techniques. In coming time we will see more devices and technologies based on spintronics.
In early 1960 Leo Esaki at IBM demonstrate that an antiferromagnetic barrier sandwiched between metal terminals displays a huge magnetoresistance. Consequent investigations of magnetic multilayers brought about the revelation of giant magnetoresistance (GMR) in late 1980.
There are many discoveries that drive the path for the development of Spintronics like : Spin Valve Technology and Giant Magnetoresistance(GMR).
Low Power Spintronics contains Active devices as well as Passive devices. The example of low power spintronics are as follows : Spin Valve Technology and Giant Magnetoresistance(GMR), FTJ (Ferroelectric Tunnel Junction), MTJ (Magnetic Tunnel Junction), DW (Domain Wall).
The revolutionary discovery of late 1980 was a Giant Magnetoresistance(GMR) by Fert and Grunberg independently. The polarization of bordering ferro-magnetic layers are having parallel alignment or having anti-parallel alignment it changes resistance(electric) in larger value. The resistance is low for parallel arrangement and high for antiparallel arrangement. The polarization can be controlled by using external field (magnetic).
(Source : http://slideplayer.com/slide/7494856/)
Giant Magnetoresistance has main application in magnetic field sensors used to make hard disks, MEMS( MicroelectroMechanical Systems) and Bio-sensors. GMR has multilayer structures. It can be used to make MRAM too. These experiments were performed with high value of magnetic fields and low values of temperature. After some years GMR in Co/Cu multilayers were discovered. These experiments were performed at room temperature and with low value magnetic field. The materials to make GMR structures are Fe/Cr or Co/Cu.
Spin Valve Technology
Spin valve is the device consists of more than two magnetic materials which are conducting. The electric resistance of Spin valve takes two values which depends on arrangement of polarization in the layers. Giant Magnetoresistance is responsible for change in it.
Spin valve is multilayer structure which has magnetic core. Top layer of it is anti-ferromagnetic. After that there is ferromagnetic layer. Now non-magnetic conducting material is between two ferromagnetic layers.
Here ferromagnetic layer which is connected to anti-ferromagnetic layer acted as fixed layer where other ferromagnetic layer which is below the non-magnetic layer acted as Free layer. When the direction of both layers is same(parallel) it has low resistance when other side when they are arranged antiparallel(opposite) it has high resistance.
There are three types of Spin valve : Bottom FM Layer Spin valve , Top FM Layer Spin Valve , Symmetrical Spin Valve
(Source: http://nptel.ac.in/courses/115103038/26 )
In Top Layer Spin valve top ferromagnetic layer acts as free layer while in Bottom Layer Spin Valve bottom ferromagnetic layer acts as free layer and in Symmetrical Spin valve middle ferromagnetic layer acts as free layer.
Magnetoresistive Random Access Memory (MRAM)
MRAM is stable random access memory which has the speed of Static Random Access Memory (SRAM) , density of Dynamic random access Memory (DRAM) , lower power requirements in writing and has unlimited write cycles. DARPA ( Defence Advanced Research Project Agency)
Started this project with the name Spintronics Project. In 1996 Motorola and Freescale developed real magnetoresistive random access memory at IBM.
Working Of MRAM
Not at all like DRAM, which utilizes electrical charge to decide whether a bit is set(1) or not set(0), magnetoresistive memory utilizes a couple of ferromagnetic metal plates isolated by a thin protecting material layer. In this arrangement one plate can polarized where other plate is always polarized and permanent magnet. This fundamental structure is known as MTJ ( Magnetic Tunnel Junction). The arrangement of these two plates characterizes that bit is set or not.
Principal of Magnetic Tunnel Junction is electron tunneling. This electron tunneling is the quantum miracle. Few nanometers thick insulating layer enables electrons to pass through itself from one plate to the other. In the event that the magnetic fields of each plate are situated in parallel or not will decide what amount tunneling will happen, and that progressions the electrical resistance of the magnetic tunnel intersection, which decides that bit is set or not.
Early MRAM(magnetoresistive random access memory) frameworks utilized currents(electrical) to initiate the field(electric) in the Magnetic Tunnel Junction to read or write the cell, however that requires more power than is perfect for current PC frameworks. Today, most exertion is being set in utilizing something many refer to as Spin Transfer Torque (STT) to peruse(read) or compose(write) a MRAM(magnetoresistive random access memory) cell.
Since magnetoresistive random access memory can perform read and compose(write) activities quicker than DRAM utilizing less power, while being a stable memory, it is viewed as a "general memory".
Spin Transfer Torque (STT)
Spin exchange torque doesn’t take a look at the charge instigated by the current of electrons starting with one layer of a MTJ(Magnetic Tunnel Junction) then onto the next, yet at the torque connected to the alterable layer by the angular momentum- or turn(spin) – of the electrons in the current. If there is a enough flow of electron from one plate to the other plate , it may lead to the change of magnetic alignment for other plate.
STT used by Magnetic Tunnel Junction draws substantially less power than an electrically initiated MTJ. What’s more, STT-MRAM can be made significantly littler, taking into consideration more noteworthy memory density in the memory gadgets that utilization it. In any case, to perform at high speeds, even STT-MRAM requires more power than is industrially possible to make it a swap for most employments of Dynamic Random Access Memory(DRAM).
In 1990 Supriyo Datta and Biswajit Das proposed Spin Transistor(Magnetically sensitive Transistor) which is still in development. While general transistors depends on the current(flow) of electron, fundamental of spintronics is electrons. We use different conditions of spin to transfer data and store the data.
The main advantage of spin transistor is that with the help of this the spin state of the electron can be detect and can be change without having electric current in the circuit. This makes hardware detection of today’s devices more smaller and more sensitive. Now as a result we can store more data in lesser required space which consumes less power and with faster transition and low cost materials. With the help of this more sensitive spin transistor the research of more sensitive automotive sensors is also increased which may lead to Eco friendly vehicles.
The other advantage of this material is that electron spin is not permanent or temporary but it is semi-permanent. By using this property we can make cheaper non-volatile storage device which doesn’t require constant flow of current to work. This is the same technology which is used in MRAM(magnetic random access memory).
It consumes less power than other Random Access Memory because the spin of electron can be controlled without power. Here current is also not constantly needed in working of the circuit. In this way it is power efficient.
Here we don’t need electric current into the working of the circuit because we need magnetic field in working of this circuit.
With the help of this technology we can make faster storage devices which are way faster than any other random access memory.
With the help of this technique we can store more information or data in small size device so it consumes less space.
This technique or say technology can be used for multi-device purposes like amplifiers.
This is more stable than any other Random Access Memory.
It is very tough to get complete spin magnetization.
It is hard to maintain Spin Magnetization for long duration with low value of magnetic field at room temperature.
The spin of the electron get disturbed because of impurities of solid and optical source.
The new field of Spintronics was conceived in the crossing point of magnetism, transport of electron, and optics. It has made business progress in a few territories and is progressing toward extra applications that depend on late essential revelations.
The field is adequately wide that there is no single focal hindrance to the utilization of these key physical standards to new gadgets. A portion of the advances that may bemost supportive would be room temperature exhibitions of infusion of about 100% spin magnetized current from a ferromagnetic metal, ferromagnetic semiconductor with low optical loss. These are, obviously, just a little determination of the conceivable territories that would tremendously affect Spintronics look into and on accomplishing the gadgets depicted here (and others).
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