1. Giant Magnetoresistance
Zachary Barnett
University of Tennessee
3/11/08

2. Outline Introduction Science of GMR Discovery of GMR
Anisotropic magnetoresistance
Giant magnetoresistance
Discovery of GMR
Fert’s and Grünberg’s original papers
Further research by IBM
Application of GMR
GMR-based spin valves in hard drives
Impact of GMR on the storage media industry

3. GMR – why is it useful?
Discovery and application of the GMR phenomenon is responsible for the ubiquitous availability of economical, high density information storage in our society.
Compact 160 GB Mp3 players and 1 TB hard drives, now widely available, owe their existence to GMR and subsequent related advances.

4. Science of GMR Anisotropic Magnetoresistance
Anisotropic Magnetoresistance – Reported in 1857 by British physicist Lord Kelvin.
When a current is passed through a magnetic conductor, resistance changes based on the relative angle between the current and the conductor’s magnetization.
Resistance increases when current is perpendicular to magnetization and decreases when current is parallel to magnetization.
Cause: electron spin-orbit coupling
Used as the basis of hard drive reading before GMR was discovered.

5. Science of GMR Giant magnetoresistance
System:
a thin layer of nonmagnetic material sandwiched between two layers of magnetic material.
Right: a Fe-Cr-Fe trilayer used in Grünberg’s original experiment.
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6. Science of GMR Mott Model
The electrical conductivity in metals can be described in terms of two largely independent conducting channels, corresponding to the up-spin and down-spin electrons, and electrical conduction occurs in parallel for the two channels.
In ferromagnetic metals the scattering rates of the up-spin and down-spin electrons are different.
(We will assume that the scattering is strong for electrons with spin antiparallel to the magnetization direction and weak for electrons with spin parallel to the magnetization direction.)

7. Science of GMR Giant magnetoresistance
Parallel magnetization
Up-spin electrons experience small resistance, down-spin electrons experience large resistance.
Total resistance is

8. Science of GMR Giant magnetoresistance
Antiparallel magnetization
Both electron spins experience small resistance in one layer and large resistance in the other.
Total resistance is

9. Science of GMR Giant Magnetoresistance
Difference in resistance is given by:

10. Discovery of GMR Fert and Grünberg
Discovered by independently by Professor Albert Fert of Université Paris-Sud in France and Professor Peter Grünberg of Forschungszentrum in Jülich, Germany.
Both groups submitted papers to Physical Review in the summer of 1988.

11. Discovery of GMR Fert 60-bilayered Fe-Cr structure at 4.2 K
Nearly 50% drop in resistance observed!!
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12. Discovery of GMR Grünberg
Fe-Cr-Fe trilayer at room temperature
1.5% drop in resistance reported
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13. Discovery of GMR IBM
Stuart Parkin of IBM attempted to reproduce the effect using the sputtering technique
Fert and Grünberg used molecular beam epitaxy, a more precise but slower and more expensive method.
Parkin’s group succeeded, observing GMR in the first multilayer sample’s produced.
Parkin’s group began experimenting with various sample compositions and layer thicknesses to better understand GMR and how to integrate it into magnetic storage.

14. GMR in practice Spin Valve
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15. GMR’s effect on hard drive industry
First GMR hard drive deployed:
Deskstar 16 GP by IBM
Date: 1997
Storage: 16.8 GB
2.7 billion bits per square inch.
Current largest hard drive:
Deskstar 7K1000 by Hitachi
Date: 2007
Storage: 1 TB
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16. References
The Class for Physics of the Royal Swedish Academy of Science. The Discovery of Giant Magnetoresistance,
E. Y. Tsymbal and D. G. Pettifor. Solid State Physics, volume 56. Academic Press, 2001.
G. Binasch et. al. Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange. Physical Review B, 61, 2472 (1989).
Charles Day. Discoverers of giant magnetoresistance win this year’s physics nobel. Physics Today, December 2007.
M. N. Baibich et. al. Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlatices. Physical Review Letters, 39, 4828 (1988).
IBM Corporation. GMR,

17. References
Western Digital. GMR Head Technology.
Western Digital. GMR Head Technology.
The New York Times. I.B.M. Set to Introduce a Disk Drive With Improved PC Storage Devices, November 10,
The Nobel Foundation. The Nobel Prize in Physics
Melissa J. Perenson. The Hard Drive Turns 50,
The Royal Swedish Academy of Science. The Nobel Prize in Physics 2007, October 9,
Hitachi. Hitachi Ships the One Terabyte Hard Drive, April 25,