A Presentation on the Giant Magneto Resistance phenomenon. Enjoy.

1. GIANT
MAGNETORESISTANCE
&
APPLICATIONS

2. Contents
Introduction
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

3. 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%

4. Remember
Hall Effect!

5. Ferromagnetic materials

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

7. Spin Dependent Conduction in Ferromagnetic Materials
ρ↓
ρ↑
Mott's Two Current model
Mott, Proc.Roy.Soc A153, 1936
Fert et al, PRL 21, 1190, 1968
α=
ρ↑
ρ↓

8. Effects of Impurities

9. 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)

10. Image courtsey nobelprize.org

11. Schematic of Magnetic Multilayer
FeFe
Cr
Formed using the Molecular beam
epitaxial growth
Fe/Cr/Fe trilayer used by P. Grünberg
Fe/Cr/Fe multilayer used by A. Fert

13. 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)

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

15. Applications

16. Read head of Magnetic
Hard drive
Spin Valve Sensors

17. CPP and CIP Geometry
Source: Seagate

18. MRAM
Advantages:
Low switching time
High data storage space
Low power required
Non-Volatile

19. Spin transistor
Initial design by Datta Das et. al. Improved by Mark Johnson
Datta, S and B. Das (1990). "Electronic analog of the electrooptic modulator"

20. 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

21. 
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.)