GIANT MAGNETORESISTANCE

& APPLICATIONS

ContentsIntroduction

Ferro magnetic materials

Spintronics Spin dependent conduction

Effect of Impurities

Interlayer Coupling

GMR

Schematics of Multilayer

Evidence of GMR

Tunnel Magnetoresistance

Application

Spin Valve

MRAM

Spin transistor

Future Works

To begin we have to go back to 1857

In 1857 Scottish scientist William Thomson, who later becomes Lord Kelvin, discovers that the application of external magnetic field to a nickel (Ni) wire increases its electric resistance.

Names the Phenomenon 'Magneto-resistance'

The resistance was not lowered by more than 5%

Remember Hall Effect!

Ferromagnetic materials

Spintronics

The idea in quantum physics that electrons have both Charge and spin.

Spin Dependent Conduction in Ferromagnetic Materials

ρ↓

ρ↑Mott's Two Current model

Mott, Proc.Roy.Soc A153, 1936Fert et al, PRL 21, 1190, 1968

α=ρ↑ρ↓

Effects of Impurities

Interlayer Coupling

Transport of spin along the interfaces results in torque acting on the magnetization which is due to the fact that majority and minority electrons have different reflection coefficients at the interfaces. The torque alignes the magnetization according to the associated ratio of reflection coefficients

P.Grünberg, R.Schreiber, Y.Pang, M.B.Brodsky and H.Sowers, Phys. Rev.Lett. 57, 2442 (1986)

Image courtsey nobelprize.org

Schematic of Magnetic MultilayerFeFe

Cr

Formed using the Molecular beam epitaxial growth

Fe/Cr/Fe trilayer used by P. Grünberg

Fe/Cr/Fe multilayer used by A. Fert

First Evidence of GMR

A. Fert and I.A. Campbell, “Two-current conduction in nickel” Phys. Rev. Lett. 21, 1190 (1968)G. Binasch, P. Grünberg, “Enhanced magnetoresistance in layered magnetic structures ”, Phys. Rev. B 39, (1989)

Tunnel Magnetoresistance

Moodera et al, Miyasaki et al, 1995CoFe/AlO /Co, MR~30% - 40%

Applications

Read head of Magnetic Hard drive

Spin Valve Sensors

CPP and CIP Geometry

Source: Seagate

MRAM

Advantages:Low switching timeHigh data storage spaceLow power requiredNon-Volatile

Spin transistorInitial design by Datta Das et. al. Improved by Mark Johnson

Datta, S and B. Das (1990). "Electronic analog of the electrooptic modulator"

Future Works

Magnetic Switching transistors and Microwave Generation By Spin Transfer

Next generation of MRAM with precise addressing and low power requirement

Self synchronous Spin Transfer Oscillators(STO) with frequency control using Dc tuning

Integration of Spintronics with semiconductors hybrid structures associating ferromagnetic metals with

nonmagnetic semiconductors. eg. Spin led, Spin solar cell fabrication of ferromagnetic semiconductors. Ga 1-x Mn x

As

In Bio-Medical Research

Future Works (Contd.)