Giant Magnetoresistance

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Giant Magnetoresistance

• Zachary Barnett
• University of Tennessee
• 3/11/08

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Outline

• Introduction
• Science of GMR
• Anisotropic magnetoresistance
• Giant magnetoresistance
• Discovery of GMR
• Ferts and Grünbergs original papers
• Further research by IBM
• Application of GMR
• GMR-based spin valves in hard drives
• Impact of GMR on the storage media industry

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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.

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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
  conductors 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.

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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 Grünbergs
  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.)

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Science of GMR Giant magnetoresistance

• Parallel magnetization
• Up-spin electrons experience small resistance,
  down-spin electrons experience large resistance.
• Total resistance is

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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

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Science of GMR Giant Magnetoresistance

• Difference in resistance is given by

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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.

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Discovery of GMR Fert

• 60-bilayered Fe-Cr structure at 4.2 K
• Nearly 50 drop in resistance observed!!

5
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Discovery of GMR Grünberg

• Fe-Cr-Fe trilayer at room temperature
• 1.5 drop in resistance reported

3
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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.
• Parkins group succeeded, observing GMR in the
  first multilayer samples produced.
• Parkins group began experimenting with various
  sample compositions and layer thicknesses to
  better understand GMR and how to integrate it
  into magnetic storage.

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GMR in practice Spin Valve
8
7.
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GMRs 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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References

1. The Class for Physics of the Royal Swedish
   Academy of Science. The Discovery of Giant
   Magnetoresistance, 2007. http//nobelprize.org/nob
   el_prizes/physics/laureates/2007/phyadv07.pdf
2. E. Y. Tsymbal and D. G. Pettifor. Solid State
   Physics, volume 56. Academic Press, 2001.
3. G. Binasch et. al. Enhanced magnetoresistance in
   layered magnetic structures with
   antiferromagnetic interlayer exchange. Physical
   Review B, 61, 2472 (1989).
4. Charles Day. Discoverers of giant
   magnetoresistance win this years physics nobel.
   Physics Today, December 2007.
5. M. N. Baibich et. al. Giant Magnetoresistance of
   (001)Fe/(001)Cr Magnetic Superlatices. Physical
   Review Letters, 39, 4828 (1988).
6. IBM Corporation. GMR, 1996. http//www.research.i
   bm.com/research/gmr.html
7. http//www.stoner.leeds.ac.uk/research/gmr.htm

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References

1. Western Digital. GMR Head Technology.
   http//www.wdc.com/en/library/2579-890043.pdf.
2. Western Digital. GMR Head Technology.
   http//www.wdc.com/en/library/2579-850121.pdf.
3. The New York Times. I.B.M. Set to Introduce a
   Disk Drive With Improved PC Storage Devices,
   November 10, 1997. http//query.nytimes.com/gst/fu
   llpage.html?res9506E7DE1339F933A25752C1A961958260
   
4. The Nobel Foundation. The Nobel Prize in Physics
   2007. http//nobelprize.org/nobel_prizes/physics/
   laureates/2007/info.pdf.
5. Melissa J. Perenson. The Hard Drive Turns 50,
   2006. http//www.pcworld.com/article/id,127104/ar
   ticle.html.
6. The Royal Swedish Academy of Science. The Nobel
   Prize in Physics 2007, October 9, 2007.
   http//nobelprize.org/nobel_prizes/physics/laureat
   es/2007/press.html.
7. Hitachi. Hitachi Ships the One Terabyte Hard
   Drive, April 25, 2007. http//www.hitachigst.com/p
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