134
R. Mattana et al.
5.1.1.2 First Observation of GMR Effects
The first studies of GMR effects were done in Fe/Cr superlattices (Fe: FM, Cr: nonFM metal). A key point of these heterostructures was the control of the magnetic
configuration. Exploiting the indirect exchange interaction between the magnetic
layers transmitted by the conduction electron (called RKKY interaction) through
the non-magnetic spacer layer, P. Grünberg and co-workers proved in 1986 that it is
possible to align the magnetization of consecutive Fe layers in opposite direction at
zero magnetic field by choosing adequate Cr interlayer thickness [6]. The parallel
magnetic configuration can then be reached by applying a large magnetic field in order
to overcome the RKKY coupling. First magnetoresistance curves have been obtained
by the groups of A. Fert in Orsay, France (Fig. 5.3 left) and P. Grünberg in Jüllich,
Germany (Fig. 5.3 right). A higher resistance state is observed at zero magnetic field
at which the antiparallel magnetic configuration is stabilized. By applying a magnetic
field, the parallel magnetic configuration is progressively reached inducing a large
decrease of the resistance. In the experiments done in Grünberg’s group, a GMR
effect of 1.5% at low temperature was obtained in the case of a Fe/Cr/Fe trilayer
(Fig. 5.3 right). The striking point is that this effect is about one order of magnitude
larger in amplitude than the anisotropic magnetoresistance of a single Fe thin film
(also shown on Fig. 5.3 right). In Fert’s group, measurements were performed in
Fe/Cr superlattices instead of trilayers, which allowed to considerably increase the
amplitude of the effect that reached 80% for sixty Fe/Cr bilayers (Fig. 5.3 left).
An important development towards the implementation of the GMR systems for
applications in read heads for hard-disk drives or sensors was made in 1991 by
B. Dieny et al. [7] at IBM who reported the first observation of GMR in simple
Fig. 5.3 Pioneer observation of GMR in Fe/Cr superlattices (left) and in Fe/Cr/Fe trilayer (right).
At zero magnetic field, magnetization of consecutive layers is pointing in opposite direction leading
to a high resistance state. By applying a magnetic field, a parallel magnetic configuration is reached
and so a low resistance state is obtained. For a Fe/Cr/Fe trilayer, the GMR ratio is about 1.5% and
one order of magnitude larger than the anisotropic magnetoresistance of a single Fe layer (right).
By using Fe/Cr superlattices (60 Fe/Cr repetitions) the GMR ratio reaches 80% at low temperature.
Reproduced from [9] (left) and [10] (right) with permission (Copyright 1988 and 1989, American
Physical Society)
R. Mattana et al.
5.1.1.2 First Observation of GMR Effects
The first studies of GMR effects were done in Fe/Cr superlattices (Fe: FM, Cr: nonFM metal). A key point of these heterostructures was the control of the magnetic
configuration. Exploiting the indirect exchange interaction between the magnetic
layers transmitted by the conduction electron (called RKKY interaction) through
the non-magnetic spacer layer, P. Grünberg and co-workers proved in 1986 that it is
possible to align the magnetization of consecutive Fe layers in opposite direction at
zero magnetic field by choosing adequate Cr interlayer thickness [6]. The parallel
magnetic configuration can then be reached by applying a large magnetic field in order
to overcome the RKKY coupling. First magnetoresistance curves have been obtained
by the groups of A. Fert in Orsay, France (Fig. 5.3 left) and P. Grünberg in Jüllich,
Germany (Fig. 5.3 right). A higher resistance state is observed at zero magnetic field
at which the antiparallel magnetic configuration is stabilized. By applying a magnetic
field, the parallel magnetic configuration is progressively reached inducing a large
decrease of the resistance. In the experiments done in Grünberg’s group, a GMR
effect of 1.5% at low temperature was obtained in the case of a Fe/Cr/Fe trilayer
(Fig. 5.3 right). The striking point is that this effect is about one order of magnitude
larger in amplitude than the anisotropic magnetoresistance of a single Fe thin film
(also shown on Fig. 5.3 right). In Fert’s group, measurements were performed in
Fe/Cr superlattices instead of trilayers, which allowed to considerably increase the
amplitude of the effect that reached 80% for sixty Fe/Cr bilayers (Fig. 5.3 left).
An important development towards the implementation of the GMR systems for
applications in read heads for hard-disk drives or sensors was made in 1991 by
B. Dieny et al. [7] at IBM who reported the first observation of GMR in simple
Fig. 5.3 Pioneer observation of GMR in Fe/Cr superlattices (left) and in Fe/Cr/Fe trilayer (right).
At zero magnetic field, magnetization of consecutive layers is pointing in opposite direction leading
to a high resistance state. By applying a magnetic field, a parallel magnetic configuration is reached
and so a low resistance state is obtained. For a Fe/Cr/Fe trilayer, the GMR ratio is about 1.5% and
one order of magnitude larger than the anisotropic magnetoresistance of a single Fe layer (right).
By using Fe/Cr superlattices (60 Fe/Cr repetitions) the GMR ratio reaches 80% at low temperature.
Reproduced from [9] (left) and [10] (right) with permission (Copyright 1988 and 1989, American
Physical Society)