PRESENTED BY:MUSTAHID ALI

ROLL NO:- 08300102033ECE

7th SEM, 4th YEAR.UTTARANCHAL INSTITUTE OF TECHNOLOGY.

SPINTRONICS

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-state devices.

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

circuit elements.

Evolution of SpintronicsSpintronics 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.

GMR(GAINT MAGNETORESISTANCE)

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.

GMRTwo 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. Eg…iron, cobalt,nickel.

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 (Ag).

(a) Intrinsic magnetic dipole moments have parallel alignment in ferromagnetic materials

(b) Anti-parallel alignment but zero magnetization in anti-ferromagnetic materials (c) Anti-parallel alignment with unequal moments in ferromagnetic materials.

Magnetic Tunneling Junctions (MTJs)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.

MJT

SPIN TORQUE EFFECTChanging of the moment by sending a

polarized current is called the spin‐torque effect, or spin transfer switching.

SPIN INJECTION INTO SEMICONDUCTORSSince 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 EffectIn 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 structures.

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.

APPLICATIONSModern 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 nanoseconds.

 Racetrack memory, encodes information in the direction of magnetization between domain walls of a ferromagnetic metal wire.

semiconductor lasers using spin-polarized electrical injection.

 spin-based transistor.