Giant Magnetoresistance

Outline
Introduction
Science of GMR
Anisotropic magnetoresistance
Giant magnetoresistance
Discovery of GMR
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
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 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.)

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

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

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
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
[7].
[8]

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