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R. Mattana et al.
Fig. 5.4 Illustration of the two-current model: conduction of an electron in a ferromagnetic
metal/normal metal/ferromagnetic metal (FM/NM/FM) multilayer. The electrons with a spin aligned
parallel (resp. anti-parallel) to the local magnetization see a resistance r (resp. R) through this
magnetic layer. The equivalent resistance circuit is presented for two configurations: consecutive
ferromagnetic layers with parallel magnetization or anti-parallel magnetization
layers, and thus the effect of short-circuit by one of the channels is suppressed. Consequently the two channels have the same resistance
R+r
2
and the total resistance is
R+r
4
, which is in general much larger than r P = r .
This brings the possibility of switching between high and low resistance states by
simply changing the relative orientation of the magnetization of consecutive layers.
If we can engineer these structures to stabilize the two (P) and (AP) magnetic states
in absence of any external field, then such system defines a magnetic bit to store
the information, using the powerful stability of the magnets, already well known
through the development of hard-disk drives. The state can then be read through a
very simple process, i.e. by measuring the resistance of the stack.
Following this model, the amplitude of the GMR ratio can be simply deduced
G M R =
R AP − R P
R P
=
(R − r )
2
4Rr
(5.1)
In short, the understanding and expertise acquired during the 60s and 70s for
tailoring the spin-transport properties combined with the development of metallic
magnetic multilayers in the 80s has led to the discovery of the GMR effect in 1988.
Less than 10 years after the discovery of the GMR effect considered as the birth
of spintronics, this effect has largely participated to the explosion of the amount of
data storage in the mid-90s through the commercialization of the first generation of
spintronic devices such as magnetic sensors used as read heads in hard-disk drives.
R. Mattana et al.
Fig. 5.4 Illustration of the two-current model: conduction of an electron in a ferromagnetic
metal/normal metal/ferromagnetic metal (FM/NM/FM) multilayer. The electrons with a spin aligned
parallel (resp. anti-parallel) to the local magnetization see a resistance r (resp. R) through this
magnetic layer. The equivalent resistance circuit is presented for two configurations: consecutive
ferromagnetic layers with parallel magnetization or anti-parallel magnetization
layers, and thus the effect of short-circuit by one of the channels is suppressed. Consequently the two channels have the same resistance
R+r
2
and the total resistance is
R+r
4
, which is in general much larger than r P = r .
This brings the possibility of switching between high and low resistance states by
simply changing the relative orientation of the magnetization of consecutive layers.
If we can engineer these structures to stabilize the two (P) and (AP) magnetic states
in absence of any external field, then such system defines a magnetic bit to store
the information, using the powerful stability of the magnets, already well known
through the development of hard-disk drives. The state can then be read through a
very simple process, i.e. by measuring the resistance of the stack.
Following this model, the amplitude of the GMR ratio can be simply deduced
G M R =
R AP − R P
R P
=
(R − r )
2
4Rr
(5.1)
In short, the understanding and expertise acquired during the 60s and 70s for
tailoring the spin-transport properties combined with the development of metallic
magnetic multilayers in the 80s has led to the discovery of the GMR effect in 1988.
Less than 10 years after the discovery of the GMR effect considered as the birth
of spintronics, this effect has largely participated to the explosion of the amount of
data storage in the mid-90s through the commercialization of the first generation of
spintronic devices such as magnetic sensors used as read heads in hard-disk drives.