ROLL NO:- 08300102033
7th SEM, 4th YEAR.
UTTARANCHAL INSTITUTE OF TECHNOLOGY.
What is Spintronics ?
Spintronics (a neologism meaning "spin transport electronics"), also
known as magneto electronics, is an emerging technology that exploits
both the intrinsic spin of the electron and its associated magnetic
moment , in addition to its fundamental electronic charge, in solid-
An additional effect occurs when a spin-polarized current is induced.
In these cases, the electron spin is quantized in the direction
perpendicular to both the plane normal and the two-dimensional wave
vector, thus splitting the energy band. This is called the Rashba effect.
Now, however, physicists are trying to exploit the ‘spin’ of the electron
rather than its charge to create a remarkable new generation of
‘spintronic’ devices which will be smaller, more versatile and more
robust than those currently making up silicon chips and
Evolution of Spintronics
Spintronics came into light by the advent of Giant
Magneto Resistance (GMR) in 1988.
It results from subtle electron – spin effects in ultra
multilayers of magnetic materials that cause a huge
change in electrical resistance.
The simplest method of generating a spin- polarised
current in a metal is to pass the current through
a ferromagnetic material. The most common application of
this effect is a giant magnetoresistance (GMR) device.
A typical GMR device consists of at least two layers of
ferromagnetic materials separated by a spacer layer. When
the two magnetization vectors of the ferromagnetic layers
are aligned, the electrical resistance will be lower (so a
higher current flows at constant voltage) than if the
ferromagnetic layers are anti-aligned. This constitutes a
magnetic field sensor.
Two variants of GMR have been applied in devices: (1)
current-in-plane (CIP), where the electric current flows
parallel to the layers and (2) current-perpendicular-to-
plane (CPP), where the electric current flows in a
direction perpendicular to the layers.
The different types of magnetism
The origins of magnetism lie in the properties of
electrons as explained by the laws of quantum physics.
Part of an electron's magnetic properties (spin
magnetism) results from its quantum mechanical spin
state, while another part results from the orbital
motion of electrons around an atom's nucleus (orbital
magnetism) and from the magnetism of the nucleus
itself (nuclear magnetism).
Ferromagnetic materials: The source of
ferromagnetism is the spin of the electron.
Paramagnetic materials: The materials which when
placed in a magnetic field acquire feeble
magnetization in the same direction as the applied
fields . Eg..platinum,aluminium.
Diamagnetic materials: The materials which when
placed in a magnetic field acquire feeble
magnetizations in a direction opposite to that of the
applied field. Eg.. bismuth (Bi), beryllium (Be), silver
(a) Intrinsic magnetic dipole moments have parallel alignment in
(b) Anti-parallel alignment but zero magnetization in anti-
(c) Anti-parallel alignment with unequal moments in ferromagnetic
Magnetic Tunneling Junctions
In a magnetic tunneling junction (MTJ), the device
which employs the tunneling magnetoresistance
effect, two magnetic layers are separated by a thin
insulating layer. If a bias is placed across the junction,
electrons will tunnel through depending on the
relative orientation of the two ferromagnetic plates.
Currently, TMR Tunnel Magnetoresistance MTJ
sensors have been used in hard drives.
SPIN TORQUE EFFECT
Changing of the moment by sending a polarized
current is called the spin‐torque effect, or spin transfer
SPIN INJECTION INTO
Since nearly all electronic components currently rely
on semiconductors, namely Silicon, it would make
sense to interface any new spintronics technology with
semiconductors as well.
Researchers have successfully injected spin polarized
current into Silicon from a ferromagnet.
Spin Hall Effect
In order to realize spintronics as a fully operational
technology, the ability to manipulate spin polarized
electrons within a conductor is necessary
The spin of an electron is coupled to its magnetic
moment, if an electric field is placed perpendicular to
the direction of current flow, the electrons’ spin degree
of freedom interacts with the field and also
experiences a Lorentz force.
Magnetic (spin) transistors
The problem with electrically based transistors is their
volatility. This is the reason why computers cannot be
instantly turned on and off.
In a magnetic transistor, magnetized ferromagnetic
layers replace the role of n and p type semiconductors.
If the two outside layers are pinned and the middle
layer allowed to be switched by an external magnetic
field, a magnetic transistor could be made, with on
and off configuration depending on the orientation of
the middle magnetized layer.
Computing with Spins
One of the most ambitious spintronic devices is the
spin-based quantum computer in solid-state
The particles that physicists call “fermions” have two
states of spin and so can assume either “up” or “down”
states, making them natural and intrinsic binary units
called quantum bits, or qubits.
It may represent arbitrary combinations of both
values—that is, an infinite number of possibilities
between 0 and 1.
Modern hard drives are based on the GMR or TMR effect.
The latest 2nd generation MRAM techniques currently
in development, which is being use of this technology.
Motorola has developed a 1st generation 256
kb MRAM, which has a read/write cycle of under 50
Racetrack memory, encodes information in the direction
of magnetization between domain walls of a
ferromagnetic metal wire.
semiconductor lasers using spin-polarized electrical