16-05-2012, 05:39 PM
Spin Valve Transistor
spin valve transistor.docx (Size: 25.46 KB / Downloads: 30)
ABSTRACT
In a world of ubiquitous presence of electrons can you imagine any other
field displacing it? It may seem peculiar, even absurd, but with the advent of
spintronics it is turning into reality.
In our conventional electronic devices we use semi conducting materials
for logical operation and magnetic materials for storage, but spintronics uses
magnetic materials for both purposes. These spintronic devices are more versatile
and faster than the present one. One such device is spin valve transistor.
Spin valve transistor is different from conventional transistor. In this for
conduction we use spin polarization of electrons. Only electrons with correct spin
polarization can travel successfully through the device. These transistors are used
in data storage, signal processing, automation and robotics with less power
consumption and results in less heat. This also finds its application in Quantum
computing, in which we use Qubits instead of bits.
INTRODUCTION:
Two experiments in 1920’s suggested spin as an additional property of the
electron. One was the closely spaced splitting of Hydrogen spectralines, called
fine structure. The other was Stern –Gerlach experiment, which in 1922 that a
beam of silver atoms directed through an inhomogeneous magnetic field would be
forced in to two beams. These pointed towards magnetism associated with the
electrons.
Spin is the root cause of magnetism that makes an electron tiny magnet.
Magnetism is already been exploited in recording devices. Where data is
recorded and stored as tiny areas of magnetized iron or chromium oxide. To
access that information the head detects the minute changes in magnetic field.
This induces corresponding changes in the head’s electrical resistance – a
phenomenon called Magneto Resistance.
EVOLUTION OF SPINTRONICS:
Spintronics came into light by the advent of Giant Magneto Resistance
(GMR) in 1988. GMR is 200 times stronger than ordinary Magneto Resistance.
It results from subtle electron – spin effects in ultra multilayers of magnetic
materials that cause a huge change in electrical resistance.
The discovery of Spin Valve Transistor (GMR in magnetic multilayers)
has let to a large number of studies on GMR systems. Usually resistance of
multilayer is measured with the Current in Plane (CIP). For instance, Read back
magnetic heads uses this property. But this suffers from several drawbacks such
as; shunting and channeling, particularly for uncoupled multilayers and for thick
spaced layers diminish the CIP magneto resistance. Diffusive surface scattering
reduces the magneto resistance for sandwiches and thin multilayers.
To erase these problems we measure with Current Perpendicular to the
Plane (CPP), mainly because electrons cross all magnetic layers, but a practical
difficulty is encountered; the perpendicular resistance of ultra thin multilayers is
too small to be measured by ordinary techniques.
spin valve transistor.docx (Size: 25.46 KB / Downloads: 30)
ABSTRACT
In a world of ubiquitous presence of electrons can you imagine any other
field displacing it? It may seem peculiar, even absurd, but with the advent of
spintronics it is turning into reality.
In our conventional electronic devices we use semi conducting materials
for logical operation and magnetic materials for storage, but spintronics uses
magnetic materials for both purposes. These spintronic devices are more versatile
and faster than the present one. One such device is spin valve transistor.
Spin valve transistor is different from conventional transistor. In this for
conduction we use spin polarization of electrons. Only electrons with correct spin
polarization can travel successfully through the device. These transistors are used
in data storage, signal processing, automation and robotics with less power
consumption and results in less heat. This also finds its application in Quantum
computing, in which we use Qubits instead of bits.
INTRODUCTION:
Two experiments in 1920’s suggested spin as an additional property of the
electron. One was the closely spaced splitting of Hydrogen spectralines, called
fine structure. The other was Stern –Gerlach experiment, which in 1922 that a
beam of silver atoms directed through an inhomogeneous magnetic field would be
forced in to two beams. These pointed towards magnetism associated with the
electrons.
Spin is the root cause of magnetism that makes an electron tiny magnet.
Magnetism is already been exploited in recording devices. Where data is
recorded and stored as tiny areas of magnetized iron or chromium oxide. To
access that information the head detects the minute changes in magnetic field.
This induces corresponding changes in the head’s electrical resistance – a
phenomenon called Magneto Resistance.
EVOLUTION OF SPINTRONICS:
Spintronics came into light by the advent of Giant Magneto Resistance
(GMR) in 1988. GMR is 200 times stronger than ordinary Magneto Resistance.
It results from subtle electron – spin effects in ultra multilayers of magnetic
materials that cause a huge change in electrical resistance.
The discovery of Spin Valve Transistor (GMR in magnetic multilayers)
has let to a large number of studies on GMR systems. Usually resistance of
multilayer is measured with the Current in Plane (CIP). For instance, Read back
magnetic heads uses this property. But this suffers from several drawbacks such
as; shunting and channeling, particularly for uncoupled multilayers and for thick
spaced layers diminish the CIP magneto resistance. Diffusive surface scattering
reduces the magneto resistance for sandwiches and thin multilayers.
To erase these problems we measure with Current Perpendicular to the
Plane (CPP), mainly because electrons cross all magnetic layers, but a practical
difficulty is encountered; the perpendicular resistance of ultra thin multilayers is
too small to be measured by ordinary techniques.