Transcript GMR_1_Presentation - University of Tennessee

Giant
Magnetoresistance
Zachary Barnett
University of Tennessee
3/11/08
Outline


Introduction
Science 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
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.

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.
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.
[3]
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 upspin 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.)
Science of GMR
Giant magnetoresistance



Parallel magnetization
Up-spin electrons
experience small
resistance, down-spin
electrons experience
large resistance.
Total resistance is
R para
2 R R

R  R
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
Rantpara  12 (R  R )
Science of GMR
Giant Magnetoresistance

Difference in resistance is given by:
1 ( R  R )

2 ( R  R )
2
R  R para  Rantipara
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.

Discovery of GMR
Fert


[5]
60-bilayered Fe-Cr
structure at 4.2 K
Nearly 50% drop in
resistance observed!!
Discovery of GMR
Grünberg


[3]
Fe-Cr-Fe trilayer at
room temperature
1.5% drop in
resistance reported
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.
GMR in practice
Spin Valve
[8]
[7].
GMR’s effect on hard drive industry

First GMR hard drive
deployed:





[11]
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
[12]
References
1.
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4.
5.
6.
7.
The Class for Physics of the Royal Swedish Academy of Science. The
Discovery of Giant Magnetoresistance, 2007.
http://nobelprize.org/nobel_prizes/physics/laureates/2007/phyadv07.pdf
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, 1996.
http://www.research.ibm.com/research/gmr.html
http://www.stoner.leeds.ac.uk/research/gmr.htm
References
8.
9.
10.
11.
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14.
Western Digital. GMR Head Technology. http://www.wdc.com/en/library/2579-890043.pdf.
Western Digital. GMR Head Technology. http://www.wdc.com/en/library/2579-850121.pdf.
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/fullpage.html?res=9506E7DE1339F933A25752C1A961958260
The Nobel Foundation. The Nobel Prize in Physics 2007.
http://nobelprize.org/nobel_prizes/physics/laureates/2007/info.pdf.
Melissa J. Perenson. The Hard Drive Turns 50, 2006.
http://www.pcworld.com/article/id,127104/article.html.
The Royal Swedish Academy of Science. The Nobel Prize in Physics 2007, October 9, 2007.
http://nobelprize.org/nobel_prizes/physics/laureates/2007/press.html.
Hitachi. Hitachi Ships the One Terabyte Hard Drive, April 25, 2007.
http://www.hitachigst.com/portal/site/en/template.MAXIMIZE/menuitem.e39dec85503c12f57d8
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