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Paris, October 1, 2003

The CNRS has attributed this year's "Medaille d'Or" (Golden Medal) to the physicist Albert Fert

The CNRS has attributed this year's "Medaille d'Or" (Golden Medal) to the physicist Albert Fert, professor at the Unité mixte de physique CNRS/Thales (associated with the Université Paris-Sud), for his discovery of Giant Magneto-Resistance (GMR) and his contribution to the development of spin electronics. This research field in nanosciences is currently experiencing a dramatic expansion. GMR has already had an important impact on information and communication technologies. In particular, this effect is at the heart of extremely sensitive magnetic read heads in the current generation of computer hard drives. Today, some 615 million such heads are produced and commercialized each year. Other sectors should benefit from applications of spin electronics, such as mobile phones, portable computers or embedded electronics.

Albert Fert marvels at many things: at landscapes from the Catalan Pyrenean mountains of his childhood, of course; at the genius of Thelonius Monk's music and Almodovar's films as well; and also, more pragmatically, at the purring noise of his computer hard disk. The enormous capacity of today's hard disks results, in an important way, from his mental meanderings as a young researcher in the 1970s, and from his discovery of Giant Magneto-Resistance (GMR) in 1988.

From fundamental physics of spins to cutting edge technology for everyday use
The introduction of GMR read heads is indeed at the origin of the considerable increase in the information storage density on a hard drive. Moreover, this discovery launched a new research area in physics: that of spin electronics (or spintronics) - and Albert Fert is playing a principal part in this blossoming field. Today new phenomena continue to appear, spawning new applications which should underscore the all-encompassing impact of this new science on XXIst century technologies.

What is spin electronics?
As Albert Fert explains, "spin electronics takes advantage of a quantum characteristic of the electron: its spin. In an oversimplified picture, it represents a miniature compass needle carried by the electron. While classical electronics guides electrons by exerting a force on their electric charge, spin electronics guides them by acting on their spin. How does one find a force which acts efficiently on electron spins? By sending these electrons through ultrathin films of ferromagnetic materials such as iron or cobalt, the electron spin may interact strongly with the magnetization of these materials. By orienting this magnetization, it is possible to act on the spin and thus to control the movement of electrons."

In the course of his fundamental studies on ferromagnetic materials at the onset of his career, Albert Fert had clarified this influence of spin on the movement of electrons. "However, the application of these ideas and the blossoming of spin electronics required technological progress, achieved only at the end of the 1980s, in the domain of ultrathin film growth and the control of artificial structures on a very small length scale", he adds. Indeed, interesting phenomena in the field of spin electronics are achieved in "magnetic nanostructures" which combine several materials in a layer-by-layer architecture on the scale of the nanometer (one millionth millimeter). The first such structures consisted of multilayered strata combining a ferromagnetic metal and a non-ferromagnetic metal. For example, iron may alternate with chromium (see Figure 1).

The beginnings of spintronics
The first manifestation of spin electronics was the giant magnetoresistance in magnetic multilayers (see Figure 2a). In the middle of the 1980s, Albert Fert, then at the Laboratoire de Physique des Solides at Orsay, began a collaboration on magnetic multilayers with Alain Friedrich, director at Thomson-CSF of a research department which mastered the Molecular Beam Epitaxy technique used to grow ultrathin layers under ultrahigh vacuum. Albert Fert recounts: "we discovered giant magnetoresistance in 1988 on multilayers of iron and chromium. For certain thicknesses of the chromium layers, the magnetizations of succeding iron layers would point in opposite directions, in an antiparallel configuration. In the 1988 experiment, we aligned these magnetizations by applying an external magnetic field and in doing so the electrical resistance of the multilayer stack dropped considerably. The amplitude of the effect surpassed all our expectations!"
The variation of a conductor's resistance due to a magnetic field is called magnetoresistance, so that the effect measured in 1988, with a much larger amplitude, was termed Giant Magneto-Resistance (GMR).

The interpretation (see Figure 2b) of the observed effects relied on previous results obtained by Albert Fert toward analysing the influence of spin on conduction in ferromagnetic metals. The experiments revealing the GMR effect, and their interpretation, were published in a Physical Review Letters article (Phys. Rev. Lett. 61, 2472, 1988) which is considered as the manifesto of spin electronics. It has been cited close to 2500 times in the scientific literature, a feat surpassed by only five other articles since the incept of this prestigious journal 50 years ago. The team of Peter Grünberg in Jülich, Germany published similar results shortly afterwards (Phys. Rev. B39, 4828, 1989) - although with more modest amplitudes of the effect. Albert Fert goes on record to say that "Grünberg and I agreed from the beginning to consider that our experiments had taken place almost simultaneously and that we thus shared the discovery of GMR."


Over 200 GB in a GMR-enabled hard drive

The GMR effect, in particular that found with a very small magnetic field in certains multilayers, immediately raised eyebrows in the industrial community. Very sensitive magnetic field sensors utilizing the effect first appeared in 1993. "However, the most important applications remained read heads for hard drives which take advantage of the difference in resistance of a multilayer (i.e. the GMR effect) to detect the small magnetic fields generated by the information written on the disk", relates Albert Fert (see Figure 3). The sensibility of GMR detection enabled a shrinking of such "writings" by a factor of 100, leading to a commensurate increase in the density of information stored on such a disk. Today nearly all hard drive heads (615 million heads per year) use GMR while the storage capacity of such drives may exceed 200GB. With densities in excess of 20Gb per square centimeter of har disk platter - the equivalent of 2500 novels per square centimeter, we are reaching the limits of classical GMR (that with current parallel to the layers). "The future generation will no doubt use other spin electronic effects such as GMR in a current-perpendicular-to-planes geometry or tunneling magnetoresistance", explains Albert Fert.

Today's spin electronics and tomorrow's memories
The discovery of GMR has initiated many reseach endeavors throughout the world and the results have rapidly confirmed the potential of utilizing the electron spin in electronics. This new domain of physics is rapidly expanding and Albert Fert is playing a major role in its development. His team at the CNRS/Thales research unit was the first in Europe to produce working "magnetic tunnel junctions" (MTJs), and has been contributing to the understanding of the underlying Tunneling Magneto-Resistance effect (TMR). An example of a significant contribution by Albert Fert to the theory of spin electronics is also the introduction of the spin accumulation concept , which today is used in many theoretical models.

"The TMR effect in magnetic tunnel junctions will eventually lead to important applications", explains Albert Fert. A MTJ is composed of two ferromagnetic layers separated by an insulating layer approximately one nanometer thick, through which electrons have a certain probability to pass owing to the tunneling effect, a quantum phenomenon. As with GMR, the resistance of the junction is different when the magnetizations of the electrodes are aligned parallel or antiparallel to one another. "This phenomenon had in fact already been observed by Michel Jullière in France in the 1970s, but the effect was forgotten since it was difficult to reproduce. Research conducted in the United States in 1995 led to the renewal of this research field as the effect was mastered. The TMR effect will soon produce important applications in the form of Magnetic Random Access Memory. The impact on the computer technologies will be tremendous", adds the Gold Medal recipient. While Dynamic Random Access Memory (DRAM) and Static Random Access Memory, which are based on semiconductors and are in use in today's computers, are volatile - the information is lost when such memories are powered down, MRAM is permanent (see Figure 4). Thanks to this property, it won't be necessary to store programs and data on the hard drive when shutting down the computer, only to reload them into memory when turning it on again. This will speed up the way we use the machine, both at startup and during use. It will also eliminate any data loss. Moreover, as opposed to semiconductor memory which uses energy even while the computer or mobile phone is asleep, MRAM only requires energy when polled. This should lead to longer battery life for such devices. "It is in fact in this realm of roaming electronics that MRAM will integrate most quickly. The introduction onto the market of such components is slated for 2004-2005. It is noteworthy that the first industrial developments of MRAM should take place in France, at Corbeil-Essonne, for the Altis consortium composed of IBM and the german Infineon, and at Crolles, near Grenoble, for the Motorola-ST Microelectronics- Philips consortium", point out Albert Fert.

The importance of MRAM in future technologies justifies the efforts undertaken by many laboratories to improve the magnetoresistance of tunnel junctions and to offer more sophisticated and better-performing devices. A prominent result of the CNRS/Thales team in this respect was the demonstration of a record TMR effect - a 20-fold increase in junction resistance from the parallel to the antiparallel configurations) which was obtained using so-called half-metallic oxides (see Figure 5). This TMR does not subsist up to room temperature for the class of oxides studied up until now - barring any possible application, but such a path remains open toward research on other materials with such remarquable spin electronic properties. Albert Fert explains: "our team is also studying a new phenomenon which could lead to interesting applications when writing MRAM-like devices. Today's technology implements writing by orienting a magnetization by applying a magnetic field thanks to an electric current along a wire. The CNRS/Thales research unit was one of the first laboratories to show that it is possible to orient the magnetization of a small element without a magnetic field, but solely by injecting a spin current in the element. This amounts to switching the magnetization by spin transfer and the phenomenon is quite promising for applications."


Toward a fusion of classical and spin electronics

An important offshoot of spin electronics today is the study of so-called hybrid structures which combine ferromagnetic materials with semiconductors. This research field, at the interface between classical and spin electronics, is undergoing dramatic development, especially in the United States and in Japan, and represents an important activity at the CNRS/Thales research unit. Various concepts have been advanced to utilize the electron spin in a semiconductor. One can imagine, for instance, a device which combines permanent information storage capabilities with optical communication on the same chip. Nevertheless, numerous fundamental problems remain unsolved. How does one inject electrons with the same spin direction in a semi-conductor from a ferromagnetic metal? How does one then manipulate these spins in the semiconductor and detect them? Albert Fert and his team are hot on the trail to providing some answers to these questions.

One goal of researchers in this domain is to control the spin of a single electron in a minute object called a "quantum box". This promising research direction should lead to the birth of a new kind of computer. Unlike a conventional computer which churns out the result of a specified set of operations given some inputed information, this quantum computer could calculate all probable outcomes on an initial set of information by trying out all possible operations. In such a computer, bits would be replaced by wavefunctions with quantum mechanical properties. "This is also one of the fascinating research perspectives within the next decade", extols Albert Fert.


From fundamental research to advanced technologies
"The first teaching which I take away from this adventure is that technological advances generally stem from fundamental research performed long ago. Giant magnetoresistance and spin electronics did not arise spontaneously in 1988", explains Albert Fert. In the 1930s, the physics Nobel laureate Sir Nevill Mott had already proposed that spin plays a role in electrical conduction. The experimental confirmation and the development of models go back 30-35 years to research performed in a few European laboratories (in Strasbourg in the François Gautier group, in Orsay with the research of Campbell and Fert, in the Netherlands at the Eindhoven laboratory). "But making artificial structures on the length scale of the nanometer was unthinkable at the time", explains Albert Fert. "The onset of GMR and spin electronics reflects a conjunction between the ideas of fundamental physics crafted in the 1970s and technological progress achieved in the 1980s in the realm of nanostructural growth techniques. Subsequent developments of spin electronics have also been tied to nanotechnological progress. In fact this problem isn't specific to spin electronics: we are witnessing the rapid expansion of other domains in condensed matter physics as these nanotechnologies mature".

For the physicist, the discovery of GMR and the subsequent developments have also underscored the interest in associating fundamental research labs from the CNRS or universities to industrial partners. "Such a marriage is interesting both due to complementary technologies from each side, and since researchers may attain a vision of today's industrial stakes while engineers may grasp the potential offered by fundamental advances. In our domain, such intermixing led to the creation of our Unité Mixte de Physique CNRS/Thales associated to the Université of Paris-Sud", points out Albert Fert, adding that "France and her european partners are not ideally positioned in the information and communication technologies. The upcoming years will no doubt bear considerable advances in these sectors which will have a profound economical impact. It is therefore all the more essential that France and Europe catch up as quickly as possible to the United States and to Japan in this field."


Translated by Martin Bowen (CNRS/Thales)




Figure 1 Fert

Figure 1
Schematic of a multilayer composed of alternating layers of iron and chromium.
This multilayer is similar to that which led to the discovery of giant magnetoresistance in 1988. Each layer is composed of three atomic layers (represented by balls) in a body-centered cubic cristal lattice.
Arrows indicate the orientation of the Fe layer magnetization with no external magnetic field applied.




Figure2 fert

Figure 2A
Evolution of electrical resistance of a Fe/Cr multilayer stack as a function of applied field - the first observation of GMR.
One kiloOersted equals one tenth of a Tesla. Schematics below the experimental data represent the configuration of adjacent Fe layer magnetizations for various values of applied field. When the Fe layer thickness is 30 Angströms (1Angström=10-10m), and that of Cr 9 Angströms, the relative variation of resistance (magnetoresistance) reaches 80%.

Figure 2B
Illustration of the GMR mechanism.
The large arrows represent the magnetizations of adjacent ferromagnetic layers. Oblique lines represent the electron trajectories. It is supposed that the latter propagate more easily within a layer when their spin represented by small horizontal arrows, is aligned parallel to the magnetization.
In the configuration labelled (a), for which the magnetizations of the ferromagnetic layers are aligned parallel, half of the electrons may propagate easily, leading to a short-circuit effect due to this conduction channel with low electrical resistance.
In the "antiparallel" configuration labelled (b), electrons from both spin directions are slowed down in alternating Fe layers: the absence of a short-circuit leads to a much higher resistance.





Figure3Fert

Figure 3
Schematic of a read head in a hard drive utilizing the GMR effect to detect minute magnetic fields generated by the information written on the platter.





Figure4Fert

Figure 4
Top: MRAM memory cells composed of a magnetic tunnel junction (MTJ). States "0" and "1" in the cells correspond to the parallel and antiparallel alignments of the electrode magnetic moments, respectively, leading to high and low resistance states.
Bottom: Schematic of a MRAM designed using MTJs connected to a grid of conducting lines called "bit" and "word" lines.
These lines enable changing the state of a cell (writing) as well as examining its state (reading) by utilizing the TMR effect.




figure5Fert

Figure 5
High-resolution transmission electron microscopy image of a magnetic tunnel junction composed of two ferromagnetic manganese oxide layers separated by an insulating layer of strontium titanate.
Atomic rows may be clearly distinguished. (Image by J-L. Maurice, CNRS/Thales).






ECONOMIC IMPACT OF SPINtrONICS

Three large areas of application are directly addressed by the development of spintronics:

  • The domain of the magnetic recording with the read heads of hard disks
  • The magnetic sensors for applications in automotive, professional but also possibly consumer products.
  • The electronic memories with the arrival on the market announced at the horizon 2004-2005 of the first generation of MRAM (Magnetic Random Access Memory).

    Magnetic recording:
  • It is historically the first sector on which the Giant MagnetoResistance effect (GMR) had a significant impact. From the end of 1997, all the read-heads of hard disks have gradually used the GMR.
  • This transition allowed to double the growth rate of the storage density up to
    120 % per year between 1998 and 2002.
  • The current market of hard disks represents approximately 50 billion euros, the read-heads representing more than 10 %.

    Magnetic sensors:
  • The first magnetoresistive sensors using the GMR were introduced in 1994 on specific markets.
  • The market of magnetoresistive sensors is complex. It is in fact a mixture of specific markets of more or less large size.
  • The applications can be grouped in three domains:
    - The detection of a magnetic field (compass, measure of electric current)
    - The detection of an object via its magnetic signature (counting of vehicles, detection of maritime ships).
    - The detection of the movement of an object containing a magnet (doors lock in aircrafts, contactless potentiometer).
  • The volume of the current market is 800-900 million euros. Its growth is widely dependent on the penetration of mass markets corresponding to automotive or consumer applications.

    Electronic memories:
  • It is the domain of application of MRAM, which should be the first product using the spin dependent tunnel effect (TMR).
  • MRAM is a technology of non volatile electronic memory, whose performances should make it competitive with regard to all current technologies of memories (DRAM, SRAM, Flash). Its only competitor as an emergent technology is the ferroelectric memory. The advantages for the MRAM are a better capacity of integration, a better access time and a better reliability.
  • The first generation of products is announced for 2004-2005. The first two industrial developments from western actors (Europe and the United States) should be located in France in Crolles (consortium between ST Microelectronics, Philips and Motorola) and in Corbeil-Essonnes (Altis consortium: IBM, Infineon). There are other actors in Asia (Japan, Korea).
  • The global market of the electronic memories in 2002 is about 25 billion euros. It divides into three sectors:
    - The memories for consumer products (organisers, cameras), for which the dominant factor is the research of a low-cost component. This sector represents 9 billion euros in 2002. We can reasonably think that it is the first one which will be addressed by MRAM products.
    - The memories for computers (DRAM, SRAM) which are the result of a compromise between performances and cost. This sector represents 15 billion euros in 2002.
    - The memories for military and spatial applications. An important characteristic in this domain is the radiation hardness of the devices.

     

  • Contacts:

    Albert Fert
    Unité mixte de physique CNRS/Thales
    Tel: +33 1 69 33 91 05
    e-mail : albert.fert@thalesgroup.com

    Communication:
    Vincent Cros
    Unité mixte de physique CNRS/Thales
    Tel : +33 1 69 33 92 31
    e-mail : vincent.cros@thalesgroup.com

    Contact CNRS Physical Sciences and Mathematics Department:
    Frédérique Laubenheimer
    Tel : +33 1 44 96 42 63
    e-mail : frederique.laubenheimer@cnrs-dir.fr

    Press contact :
    Muriel Ilous
    Tel : +33 1 44 96 43 09
    e-mail : muriel.ilous@cnrs-dir.fr


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